| Message ID | 20240321101532.59272-2-xuanzhuo@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | refactor the params of find_vqs() | expand |
On 21.03.24 11:15, Xuan Zhuo wrote: > Currently, the init_vqs function within the virtio_balloon driver relies > on the condition that certain names array entries are null in order to > skip the initialization of some virtual queues (vqs). This behavior is > unique to this part of the codebase. In an upcoming commit, we plan to > eliminate this dependency by removing the function entirely. Therefore, > with this change, we are ensuring that the virtio_balloon no longer > depends on the aforementioned function. > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> > --- > drivers/virtio/virtio_balloon.c | 41 +++++++++++++++------------------ > 1 file changed, 19 insertions(+), 22 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 1f5b3dd31fcf..becc12a05407 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -531,49 +531,46 @@ static int init_vqs(struct virtio_balloon *vb) > struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX]; > vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX]; > const char *names[VIRTIO_BALLOON_VQ_MAX]; > - int err; > + int err, nvqs, idx; > > - /* > - * Inflateq and deflateq are used unconditionally. The names[] > - * will be NULL if the related feature is not enabled, which will > - * cause no allocation for the corresponding virtqueue in find_vqs. > - */ > callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack; > names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate"; > callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack; > names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate"; I'd remove the static dependencies here completely and do it consistently: nvqs = 0; callbacks[nvqs] = balloon_ack; names[nvqs++] = "inflate"; callbacks[nvqs] = balloon_ack; names[nvqs++] = "deflate"; > - callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL; > - names[VIRTIO_BALLOON_VQ_STATS] = NULL; > - callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; > - names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; > - names[VIRTIO_BALLOON_VQ_REPORTING] = NULL; > + > + nvqs = VIRTIO_BALLOON_VQ_DEFLATE + 1; > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { > - names[VIRTIO_BALLOON_VQ_STATS] = "stats"; > - callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request; > + names[nvqs] = "stats"; > + callbacks[nvqs] = stats_request; > + ++nvqs; callbacks[nvqs++] = stats_request; If you prefer to keep it separate, "nvqs++" please. ... same here: idx = 0; vb->inflate_vq = vqs[idx++]; vb->deflate_vq = vqs[idx++]; ... > > vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; > vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; > + > + idx = VIRTIO_BALLOON_VQ_DEFLATE + 1; > + > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { > struct scatterlist sg; > unsigned int num_stats; > - vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS]; > + vb->stats_vq = vqs[idx++]; > > /* > * Prime this virtqueue with one buffer so the hypervisor can > @@ -593,10 +590,10 @@ static int init_vqs(struct virtio_balloon *vb) > } > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > - vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE]; > + vb->free_page_vq = vqs[idx++]; > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) > - vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING]; > + vb->reporting_vq = vqs[idx++]; > Apart from that LGTM
On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > Currently, the init_vqs function within the virtio_balloon driver relies > on the condition that certain names array entries are null in order to > skip the initialization of some virtual queues (vqs). This behavior is > unique to this part of the codebase. In an upcoming commit, we plan to > eliminate this dependency by removing the function entirely. Therefore, > with this change, we are ensuring that the virtio_balloon no longer > depends on the aforementioned function. This is a behavior change, and I believe means that the driver no longer follows the spec [1]. For example, the spec says that virtqueue 4 is reporting_vq, and reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, but there is no mention of its virtqueue number changing if other features are not set. If a device/driver combination negotiates VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is that reporting_vq should still be vq number 4, and vq 2 and 3 should be unused. This patch would make the reporting_vq use vq 2 instead in this case. If the new behavior is truly intended, then the spec does not match reality, and it would need to be changed first (IMO); however, changing the spec would mean that any devices implemented correctly per the previous spec would now be wrong, so some kind of mechanism for detecting the new behavior would be warranted, e.g. a new non-device-specific virtio feature flag. I have brought this up previously on the virtio-comment list [2], but it did not receive any satisfying answers at that time. Thanks, -- Daniel [1]: https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-3140005 [2]: https://lists.oasis-open.org/archives/virtio-comment/202308/msg00280.html
On 22.03.24 20:16, Daniel Verkamp wrote: > On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: >> >> Currently, the init_vqs function within the virtio_balloon driver relies >> on the condition that certain names array entries are null in order to >> skip the initialization of some virtual queues (vqs). This behavior is >> unique to this part of the codebase. In an upcoming commit, we plan to >> eliminate this dependency by removing the function entirely. Therefore, >> with this change, we are ensuring that the virtio_balloon no longer >> depends on the aforementioned function. > > This is a behavior change, and I believe means that the driver no > longer follows the spec [1]. > > For example, the spec says that virtqueue 4 is reporting_vq, and > reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, > but there is no mention of its virtqueue number changing if other > features are not set. If a device/driver combination negotiates > VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or > VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is > that reporting_vq should still be vq number 4, and vq 2 and 3 should > be unused. This patch would make the reporting_vq use vq 2 instead in > this case. > > If the new behavior is truly intended, then the spec does not match > reality, and it would need to be changed first (IMO); however, > changing the spec would mean that any devices implemented correctly > per the previous spec would now be wrong, so some kind of mechanism > for detecting the new behavior would be warranted, e.g. a new > non-device-specific virtio feature flag. > > I have brought this up previously on the virtio-comment list [2], but > it did not receive any satisfying answers at that time. Rings a bell, but staring at this patch, I thought that there would be no behavioral change. Maybe I missed it :/ I stared at virtio_ccw_find_vqs(), and it contains: for (i = 0; i < nvqs; ++i) { if (!names[i]) { vqs[i] = NULL; continue; } vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], names[i], ctx ? ctx[i] : false, ccw); if (IS_ERR(vqs[i])) { ret = PTR_ERR(vqs[i]); vqs[i] = NULL; goto out; } } We increment queue_idx only if an entry was not NULL. SO I thought no behavioral change? (at least on s390x :) ) It's late here in Germany, so maybe I'm missing something.
On Fri, 22 Mar 2024 12:56:46 +0100, David Hildenbrand <david@redhat.com> wrote: > On 21.03.24 11:15, Xuan Zhuo wrote: > > Currently, the init_vqs function within the virtio_balloon driver relies > > on the condition that certain names array entries are null in order to > > skip the initialization of some virtual queues (vqs). This behavior is > > unique to this part of the codebase. In an upcoming commit, we plan to > > eliminate this dependency by removing the function entirely. Therefore, > > with this change, we are ensuring that the virtio_balloon no longer > > depends on the aforementioned function. > > > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> > > --- > > drivers/virtio/virtio_balloon.c | 41 +++++++++++++++------------------ > > 1 file changed, 19 insertions(+), 22 deletions(-) > > > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > > index 1f5b3dd31fcf..becc12a05407 100644 > > --- a/drivers/virtio/virtio_balloon.c > > +++ b/drivers/virtio/virtio_balloon.c > > @@ -531,49 +531,46 @@ static int init_vqs(struct virtio_balloon *vb) > > struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX]; > > vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX]; > > const char *names[VIRTIO_BALLOON_VQ_MAX]; > > - int err; > > + int err, nvqs, idx; > > > > - /* > > - * Inflateq and deflateq are used unconditionally. The names[] > > - * will be NULL if the related feature is not enabled, which will > > - * cause no allocation for the corresponding virtqueue in find_vqs. > > - */ > > callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack; > > names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate"; > > callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack; > > names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate"; > > I'd remove the static dependencies here completely and do it > consistently: > > nvqs = 0; > > callbacks[nvqs] = balloon_ack; > names[nvqs++] = "inflate"; > callbacks[nvqs] = balloon_ack; > names[nvqs++] = "deflate"; > > > > - callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL; > > - names[VIRTIO_BALLOON_VQ_STATS] = NULL; > > - callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; > > - names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; > > - names[VIRTIO_BALLOON_VQ_REPORTING] = NULL; > > + > > + nvqs = VIRTIO_BALLOON_VQ_DEFLATE + 1; > > > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { > > - names[VIRTIO_BALLOON_VQ_STATS] = "stats"; > > - callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request; > > + names[nvqs] = "stats"; > > + callbacks[nvqs] = stats_request; > > + ++nvqs; > > callbacks[nvqs++] = stats_request; > > If you prefer to keep it separate, "nvqs++" please. > > ... same here: > > idx = 0; > vb->inflate_vq = vqs[idx++]; > vb->deflate_vq = vqs[idx++]; > > ... > > > > > vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; > > vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; > > + > > + idx = VIRTIO_BALLOON_VQ_DEFLATE + 1; > > + > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { > > struct scatterlist sg; > > unsigned int num_stats; > > - vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS]; > > + vb->stats_vq = vqs[idx++]; > > > > /* > > * Prime this virtqueue with one buffer so the hypervisor can > > @@ -593,10 +590,10 @@ static int init_vqs(struct virtio_balloon *vb) > > } > > > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > > - vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE]; > > + vb->free_page_vq = vqs[idx++]; > > > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) > > - vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING]; > > + vb->reporting_vq = vqs[idx++]; > > > > Apart from that LGTM Will fix in next version. Thanks. > > -- > Cheers, > > David / dhildenb >
On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: > On 22.03.24 20:16, Daniel Verkamp wrote: > > On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > >> > >> Currently, the init_vqs function within the virtio_balloon driver relies > >> on the condition that certain names array entries are null in order to > >> skip the initialization of some virtual queues (vqs). This behavior is > >> unique to this part of the codebase. In an upcoming commit, we plan to > >> eliminate this dependency by removing the function entirely. Therefore, > >> with this change, we are ensuring that the virtio_balloon no longer > >> depends on the aforementioned function. > > > > This is a behavior change, and I believe means that the driver no > > longer follows the spec [1]. > > > > For example, the spec says that virtqueue 4 is reporting_vq, and > > reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, > > but there is no mention of its virtqueue number changing if other > > features are not set. If a device/driver combination negotiates > > VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or > > VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is > > that reporting_vq should still be vq number 4, and vq 2 and 3 should > > be unused. This patch would make the reporting_vq use vq 2 instead in > > this case. > > > > If the new behavior is truly intended, then the spec does not match > > reality, and it would need to be changed first (IMO); however, > > changing the spec would mean that any devices implemented correctly > > per the previous spec would now be wrong, so some kind of mechanism > > for detecting the new behavior would be warranted, e.g. a new > > non-device-specific virtio feature flag. > > > > I have brought this up previously on the virtio-comment list [2], but > > it did not receive any satisfying answers at that time. > > Rings a bell, but staring at this patch, I thought that there would be > no behavioral change. Maybe I missed it :/ > > I stared at virtio_ccw_find_vqs(), and it contains: > > for (i = 0; i < nvqs; ++i) { > if (!names[i]) { > vqs[i] = NULL; > continue; > } > > vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], > names[i], ctx ? ctx[i] : false, > ccw); > if (IS_ERR(vqs[i])) { > ret = PTR_ERR(vqs[i]); > vqs[i] = NULL; > goto out; > } > } > > We increment queue_idx only if an entry was not NULL. SO I thought no > behavioral change? (at least on s390x :) ) > > It's late here in Germany, so maybe I'm missing something. I think we've encountered a tricky issue. Currently, all transports handle queue id by incrementing them in order, without skipping any queue id. So, I'm quite surprised that my changes would affect the spec. The fact that the 'names' value is null is just a small trick in the Linux kernel implementation and should not have an impact on the queue id. I believe that my recent modification will not affect the spec. So, let's consider the issues with this patch set separately for now. Regarding the Memory Balloon Device, it has been operational for many years, and perhaps we should add to the spec that if a certain vq does not exist, then subsequent vqs will take over its id. Thanks. > > -- > Cheers, > > David / dhildenb >
On 25.03.24 07:08, Xuan Zhuo wrote: > On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: >> On 22.03.24 20:16, Daniel Verkamp wrote: >>> On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: >>>> >>>> Currently, the init_vqs function within the virtio_balloon driver relies >>>> on the condition that certain names array entries are null in order to >>>> skip the initialization of some virtual queues (vqs). This behavior is >>>> unique to this part of the codebase. In an upcoming commit, we plan to >>>> eliminate this dependency by removing the function entirely. Therefore, >>>> with this change, we are ensuring that the virtio_balloon no longer >>>> depends on the aforementioned function. >>> >>> This is a behavior change, and I believe means that the driver no >>> longer follows the spec [1]. >>> >>> For example, the spec says that virtqueue 4 is reporting_vq, and >>> reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, >>> but there is no mention of its virtqueue number changing if other >>> features are not set. If a device/driver combination negotiates >>> VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or >>> VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is >>> that reporting_vq should still be vq number 4, and vq 2 and 3 should >>> be unused. This patch would make the reporting_vq use vq 2 instead in >>> this case. >>> >>> If the new behavior is truly intended, then the spec does not match >>> reality, and it would need to be changed first (IMO); however, >>> changing the spec would mean that any devices implemented correctly >>> per the previous spec would now be wrong, so some kind of mechanism >>> for detecting the new behavior would be warranted, e.g. a new >>> non-device-specific virtio feature flag. >>> >>> I have brought this up previously on the virtio-comment list [2], but >>> it did not receive any satisfying answers at that time. >> >> Rings a bell, but staring at this patch, I thought that there would be >> no behavioral change. Maybe I missed it :/ >> >> I stared at virtio_ccw_find_vqs(), and it contains: >> >> for (i = 0; i < nvqs; ++i) { >> if (!names[i]) { >> vqs[i] = NULL; >> continue; >> } >> >> vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], >> names[i], ctx ? ctx[i] : false, >> ccw); >> if (IS_ERR(vqs[i])) { >> ret = PTR_ERR(vqs[i]); >> vqs[i] = NULL; >> goto out; >> } >> } >> >> We increment queue_idx only if an entry was not NULL. SO I thought no >> behavioral change? (at least on s390x :) ) >> >> It's late here in Germany, so maybe I'm missing something. > > I think we've encountered a tricky issue. Currently, all transports handle queue > id by incrementing them in order, without skipping any queue id. So, I'm quite > surprised that my changes would affect the spec. The fact that the > 'names' value is null is just a small trick in the Linux kernel implementation > and should not have an impact on the queue id. > > I believe that my recent modification will not affect the spec. So, let's > consider the issues with this patch set separately for now. Regarding the Memory > Balloon Device, it has been operational for many years, and perhaps we should > add to the spec that if a certain vq does not exist, then subsequent vqs will > take over its id. Right, if I am not missing something your patch should have no functional change in that regard (that the current behavior/implementation might not match the spec is a different discussion). @Daniel, if I'm missing something, please shout.
On Mon, Mar 25 2024, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: >> On 22.03.24 20:16, Daniel Verkamp wrote: >> > On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: >> >> >> >> Currently, the init_vqs function within the virtio_balloon driver relies >> >> on the condition that certain names array entries are null in order to >> >> skip the initialization of some virtual queues (vqs). This behavior is >> >> unique to this part of the codebase. In an upcoming commit, we plan to >> >> eliminate this dependency by removing the function entirely. Therefore, >> >> with this change, we are ensuring that the virtio_balloon no longer >> >> depends on the aforementioned function. >> > >> > This is a behavior change, and I believe means that the driver no >> > longer follows the spec [1]. >> > >> > For example, the spec says that virtqueue 4 is reporting_vq, and >> > reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, >> > but there is no mention of its virtqueue number changing if other >> > features are not set. If a device/driver combination negotiates >> > VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or >> > VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is >> > that reporting_vq should still be vq number 4, and vq 2 and 3 should >> > be unused. This patch would make the reporting_vq use vq 2 instead in >> > this case. >> > >> > If the new behavior is truly intended, then the spec does not match >> > reality, and it would need to be changed first (IMO); however, >> > changing the spec would mean that any devices implemented correctly >> > per the previous spec would now be wrong, so some kind of mechanism >> > for detecting the new behavior would be warranted, e.g. a new >> > non-device-specific virtio feature flag. >> > >> > I have brought this up previously on the virtio-comment list [2], but >> > it did not receive any satisfying answers at that time. I had missed it back then, but now that I read it, I realize that we really have a bit of a mess here :/ >> >> Rings a bell, but staring at this patch, I thought that there would be >> no behavioral change. Maybe I missed it :/ >> >> I stared at virtio_ccw_find_vqs(), and it contains: >> >> for (i = 0; i < nvqs; ++i) { >> if (!names[i]) { >> vqs[i] = NULL; >> continue; >> } >> >> vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], >> names[i], ctx ? ctx[i] : false, >> ccw); >> if (IS_ERR(vqs[i])) { >> ret = PTR_ERR(vqs[i]); >> vqs[i] = NULL; >> goto out; >> } >> } >> >> We increment queue_idx only if an entry was not NULL. SO I thought no >> behavioral change? (at least on s390x :) ) The code for pci behaves in the same way. >> >> It's late here in Germany, so maybe I'm missing something. > > I think we've encountered a tricky issue. Currently, all transports handle queue > id by incrementing them in order, without skipping any queue id. So, I'm quite > surprised that my changes would affect the spec. The fact that the > 'names' value is null is just a small trick in the Linux kernel implementation > and should not have an impact on the queue id. > > I believe that my recent modification will not affect the spec. So, let's > consider the issues with this patch set separately for now. Regarding the Memory > Balloon Device, it has been operational for many years, and perhaps we should > add to the spec that if a certain vq does not exist, then subsequent vqs will > take over its id. The changes here do not really seem to affect the spec issue that Daniel had noted, unless I'm reading the code wrong. However, we should try to address the spec mess, where we have at least some of the most popular/important implementations behaving differently than the spec describes... I would suggest to discuss that on the virtio lists -- but they are still dead, and at this point I'm just hoping they'll come back eventually :/
On Mon, Mar 25, 2024 at 5:44 PM Cornelia Huck <cohuck@redhat.com> wrote: > > On Mon, Mar 25 2024, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > > On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: > >> On 22.03.24 20:16, Daniel Verkamp wrote: > >> > On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > >> >> > >> >> Currently, the init_vqs function within the virtio_balloon driver relies > >> >> on the condition that certain names array entries are null in order to > >> >> skip the initialization of some virtual queues (vqs). This behavior is > >> >> unique to this part of the codebase. In an upcoming commit, we plan to > >> >> eliminate this dependency by removing the function entirely. Therefore, > >> >> with this change, we are ensuring that the virtio_balloon no longer > >> >> depends on the aforementioned function. > >> > > >> > This is a behavior change, and I believe means that the driver no > >> > longer follows the spec [1]. > >> > > >> > For example, the spec says that virtqueue 4 is reporting_vq, and > >> > reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, > >> > but there is no mention of its virtqueue number changing if other > >> > features are not set. If a device/driver combination negotiates > >> > VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or > >> > VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is > >> > that reporting_vq should still be vq number 4, and vq 2 and 3 should > >> > be unused. This patch would make the reporting_vq use vq 2 instead in > >> > this case. > >> > > >> > If the new behavior is truly intended, then the spec does not match > >> > reality, and it would need to be changed first (IMO); however, > >> > changing the spec would mean that any devices implemented correctly > >> > per the previous spec would now be wrong, so some kind of mechanism > >> > for detecting the new behavior would be warranted, e.g. a new > >> > non-device-specific virtio feature flag. > >> > > >> > I have brought this up previously on the virtio-comment list [2], but > >> > it did not receive any satisfying answers at that time. > > I had missed it back then, but now that I read it, I realize that we > really have a bit of a mess here :/ > > >> > >> Rings a bell, but staring at this patch, I thought that there would be > >> no behavioral change. Maybe I missed it :/ > >> > >> I stared at virtio_ccw_find_vqs(), and it contains: > >> > >> for (i = 0; i < nvqs; ++i) { > >> if (!names[i]) { > >> vqs[i] = NULL; > >> continue; > >> } > >> > >> vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], > >> names[i], ctx ? ctx[i] : false, > >> ccw); > >> if (IS_ERR(vqs[i])) { > >> ret = PTR_ERR(vqs[i]); > >> vqs[i] = NULL; > >> goto out; > >> } > >> } > >> > >> We increment queue_idx only if an entry was not NULL. SO I thought no > >> behavioral change? (at least on s390x :) ) > > The code for pci behaves in the same way. > > >> > >> It's late here in Germany, so maybe I'm missing something. > > > > I think we've encountered a tricky issue. Currently, all transports handle queue > > id by incrementing them in order, without skipping any queue id. So, I'm quite > > surprised that my changes would affect the spec. The fact that the > > 'names' value is null is just a small trick in the Linux kernel implementation > > and should not have an impact on the queue id. > > > > I believe that my recent modification will not affect the spec. So, let's > > consider the issues with this patch set separately for now. Regarding the Memory > > Balloon Device, it has been operational for many years, and perhaps we should > > add to the spec that if a certain vq does not exist, then subsequent vqs will > > take over its id. > > The changes here do not really seem to affect the spec issue that Daniel > had noted, unless I'm reading the code wrong. Spec seems to be wrong here: 5.5.2 Virtqueues 0 inflateq 1 deflateq 2 statsq 3 free_page_vq4 r eporting_vq And this is the Qemu implementation: 5.5.2 Virtqueues s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, virtio_balloon_handle_free_page_vq); precopy_add_notifier(&s->free_page_hint_notify); object_ref(OBJECT(s->iothread)); s->free_page_bh = aio_bh_new_guarded(iothread_get_aio_context(s->iothread), virtio_ballloon_get_free_page_hints, s, &dev->mem_reentrancy_guard); } if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) { s->reporting_vq = virtio_add_queue(vdev, 32, virtio_balloon_handle_report); } We need to fix it. > > However, we should try to address the spec mess, where we have at least > some of the most popular/important implementations behaving differently > than the spec describes... I would suggest to discuss that on the virtio > lists -- but they are still dead, and at this point I'm just hoping > they'll come back eventually :/ > Thanks
On Tue, Mar 26, 2024 at 12:11 PM Jason Wang <jasowang@redhat.com> wrote: > > On Mon, Mar 25, 2024 at 5:44 PM Cornelia Huck <cohuck@redhat.com> wrote: > > > > On Mon, Mar 25 2024, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > > > > On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: > > >> On 22.03.24 20:16, Daniel Verkamp wrote: > > >> > On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > >> >> > > >> >> Currently, the init_vqs function within the virtio_balloon driver relies > > >> >> on the condition that certain names array entries are null in order to > > >> >> skip the initialization of some virtual queues (vqs). This behavior is > > >> >> unique to this part of the codebase. In an upcoming commit, we plan to > > >> >> eliminate this dependency by removing the function entirely. Therefore, > > >> >> with this change, we are ensuring that the virtio_balloon no longer > > >> >> depends on the aforementioned function. > > >> > > > >> > This is a behavior change, and I believe means that the driver no > > >> > longer follows the spec [1]. > > >> > > > >> > For example, the spec says that virtqueue 4 is reporting_vq, and > > >> > reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, > > >> > but there is no mention of its virtqueue number changing if other > > >> > features are not set. If a device/driver combination negotiates > > >> > VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or > > >> > VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is > > >> > that reporting_vq should still be vq number 4, and vq 2 and 3 should > > >> > be unused. This patch would make the reporting_vq use vq 2 instead in > > >> > this case. > > >> > > > >> > If the new behavior is truly intended, then the spec does not match > > >> > reality, and it would need to be changed first (IMO); however, > > >> > changing the spec would mean that any devices implemented correctly > > >> > per the previous spec would now be wrong, so some kind of mechanism > > >> > for detecting the new behavior would be warranted, e.g. a new > > >> > non-device-specific virtio feature flag. > > >> > > > >> > I have brought this up previously on the virtio-comment list [2], but > > >> > it did not receive any satisfying answers at that time. > > > > I had missed it back then, but now that I read it, I realize that we > > really have a bit of a mess here :/ > > > > >> > > >> Rings a bell, but staring at this patch, I thought that there would be > > >> no behavioral change. Maybe I missed it :/ > > >> > > >> I stared at virtio_ccw_find_vqs(), and it contains: > > >> > > >> for (i = 0; i < nvqs; ++i) { > > >> if (!names[i]) { > > >> vqs[i] = NULL; > > >> continue; > > >> } > > >> > > >> vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], > > >> names[i], ctx ? ctx[i] : false, > > >> ccw); > > >> if (IS_ERR(vqs[i])) { > > >> ret = PTR_ERR(vqs[i]); > > >> vqs[i] = NULL; > > >> goto out; > > >> } > > >> } > > >> > > >> We increment queue_idx only if an entry was not NULL. SO I thought no > > >> behavioral change? (at least on s390x :) ) > > > > The code for pci behaves in the same way. > > > > >> > > >> It's late here in Germany, so maybe I'm missing something. > > > > > > I think we've encountered a tricky issue. Currently, all transports handle queue > > > id by incrementing them in order, without skipping any queue id. So, I'm quite > > > surprised that my changes would affect the spec. The fact that the > > > 'names' value is null is just a small trick in the Linux kernel implementation > > > and should not have an impact on the queue id. > > > > > > I believe that my recent modification will not affect the spec. So, let's > > > consider the issues with this patch set separately for now. Regarding the Memory > > > Balloon Device, it has been operational for many years, and perhaps we should > > > add to the spec that if a certain vq does not exist, then subsequent vqs will > > > take over its id. > > > > The changes here do not really seem to affect the spec issue that Daniel > > had noted, unless I'm reading the code wrong. > > Spec seems to be wrong here: > > 5.5.2 Virtqueues > > 0 inflateq 1 deflateq 2 statsq 3 free_page_vq4 r eporting_vq > > And this is the Qemu implementation: > > 5.5.2 Virtqueues > > s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > > if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, > virtio_balloon_handle_free_page_vq); > precopy_add_notifier(&s->free_page_hint_notify); > > object_ref(OBJECT(s->iothread)); > s->free_page_bh = > aio_bh_new_guarded(iothread_get_aio_context(s->iothread), > > virtio_ballloon_get_free_page_hints, s, > &dev->mem_reentrancy_guard); > } > > if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) { > s->reporting_vq = virtio_add_queue(vdev, 32, > virtio_balloon_handle_report); > } > > We need to fix it. Another possible issue: FS device: 5.11.2 Virtqueues 0 hiprio 1 notification queue 2…n request queues The notification queue only exists if VIRTIO_FS_F_NOTIFICATION is set. Kernel driver had this: enum { VQ_HIPRIO, VQ_REQUEST }; Which means request starts from 1. Thanks > > > > > However, we should try to address the spec mess, where we have at least > > some of the most popular/important implementations behaving differently > > than the spec describes... I would suggest to discuss that on the virtio > > lists -- but they are still dead, and at this point I'm just hoping > > they'll come back eventually :/ > > > > Thanks
On Mon, Mar 25, 2024 at 2:11 AM David Hildenbrand <david@redhat.com> wrote: > > On 25.03.24 07:08, Xuan Zhuo wrote: > > On Fri, 22 Mar 2024 22:02:27 +0100, David Hildenbrand <david@redhat.com> wrote: > >> On 22.03.24 20:16, Daniel Verkamp wrote: > >>> On Thu, Mar 21, 2024 at 3:16 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > >>>> > >>>> Currently, the init_vqs function within the virtio_balloon driver relies > >>>> on the condition that certain names array entries are null in order to > >>>> skip the initialization of some virtual queues (vqs). This behavior is > >>>> unique to this part of the codebase. In an upcoming commit, we plan to > >>>> eliminate this dependency by removing the function entirely. Therefore, > >>>> with this change, we are ensuring that the virtio_balloon no longer > >>>> depends on the aforementioned function. > >>> > >>> This is a behavior change, and I believe means that the driver no > >>> longer follows the spec [1]. > >>> > >>> For example, the spec says that virtqueue 4 is reporting_vq, and > >>> reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set, > >>> but there is no mention of its virtqueue number changing if other > >>> features are not set. If a device/driver combination negotiates > >>> VIRTIO_BALLOON_F_PAGE_REPORTING but not VIRTIO_BALLOON_F_STATS_VQ or > >>> VIRTIO_BALLOON_F_FREE_PAGE_HINT, my reading of the specification is > >>> that reporting_vq should still be vq number 4, and vq 2 and 3 should > >>> be unused. This patch would make the reporting_vq use vq 2 instead in > >>> this case. > >>> > >>> If the new behavior is truly intended, then the spec does not match > >>> reality, and it would need to be changed first (IMO); however, > >>> changing the spec would mean that any devices implemented correctly > >>> per the previous spec would now be wrong, so some kind of mechanism > >>> for detecting the new behavior would be warranted, e.g. a new > >>> non-device-specific virtio feature flag. > >>> > >>> I have brought this up previously on the virtio-comment list [2], but > >>> it did not receive any satisfying answers at that time. > >> > >> Rings a bell, but staring at this patch, I thought that there would be > >> no behavioral change. Maybe I missed it :/ > >> > >> I stared at virtio_ccw_find_vqs(), and it contains: > >> > >> for (i = 0; i < nvqs; ++i) { > >> if (!names[i]) { > >> vqs[i] = NULL; > >> continue; > >> } > >> > >> vqs[i] = virtio_ccw_setup_vq(vdev, queue_idx++, callbacks[i], > >> names[i], ctx ? ctx[i] : false, > >> ccw); > >> if (IS_ERR(vqs[i])) { > >> ret = PTR_ERR(vqs[i]); > >> vqs[i] = NULL; > >> goto out; > >> } > >> } > >> > >> We increment queue_idx only if an entry was not NULL. SO I thought no > >> behavioral change? (at least on s390x :) ) > >> > >> It's late here in Germany, so maybe I'm missing something. > > > > I think we've encountered a tricky issue. Currently, all transports handle queue > > id by incrementing them in order, without skipping any queue id. So, I'm quite > > surprised that my changes would affect the spec. The fact that the > > 'names' value is null is just a small trick in the Linux kernel implementation > > and should not have an impact on the queue id. > > > > I believe that my recent modification will not affect the spec. So, let's > > consider the issues with this patch set separately for now. Regarding the Memory > > Balloon Device, it has been operational for many years, and perhaps we should > > add to the spec that if a certain vq does not exist, then subsequent vqs will > > take over its id. > > Right, if I am not missing something your patch should have no > functional change in that regard (that the current > behavior/implementation might not match the spec is a different discussion). > > @Daniel, if I'm missing something, please shout. Thanks for digging into that - I think you're correct in that the patch does not change the behavior, due to changes elsewhere in the generic virtio and virtio-pci code. So in that sense, I guess this should not block this particular patch. It would be good to have the spec situation cleared up, though - I guess in practice, all relevant drivers and device implementations are already following the model where there are no gaps in the queue numbering, rather than what the spec seems to indicate. Thanks, -- Daniel
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 1f5b3dd31fcf..becc12a05407 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -531,49 +531,46 @@ static int init_vqs(struct virtio_balloon *vb) struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX]; vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX]; const char *names[VIRTIO_BALLOON_VQ_MAX]; - int err; + int err, nvqs, idx; - /* - * Inflateq and deflateq are used unconditionally. The names[] - * will be NULL if the related feature is not enabled, which will - * cause no allocation for the corresponding virtqueue in find_vqs. - */ callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack; names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate"; callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack; names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate"; - callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL; - names[VIRTIO_BALLOON_VQ_STATS] = NULL; - callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; - names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; - names[VIRTIO_BALLOON_VQ_REPORTING] = NULL; + + nvqs = VIRTIO_BALLOON_VQ_DEFLATE + 1; if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { - names[VIRTIO_BALLOON_VQ_STATS] = "stats"; - callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request; + names[nvqs] = "stats"; + callbacks[nvqs] = stats_request; + ++nvqs; } if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { - names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq"; - callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; + names[nvqs] = "free_page_vq"; + callbacks[nvqs] = NULL; + ++nvqs; } if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { - names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq"; - callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack; + names[nvqs] = "reporting_vq"; + callbacks[nvqs] = balloon_ack; + ++nvqs; } - err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs, - callbacks, names, NULL); + err = virtio_find_vqs(vb->vdev, nvqs, vqs, callbacks, names, NULL); if (err) return err; vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; + + idx = VIRTIO_BALLOON_VQ_DEFLATE + 1; + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { struct scatterlist sg; unsigned int num_stats; - vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS]; + vb->stats_vq = vqs[idx++]; /* * Prime this virtqueue with one buffer so the hypervisor can @@ -593,10 +590,10 @@ static int init_vqs(struct virtio_balloon *vb) } if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) - vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE]; + vb->free_page_vq = vqs[idx++]; if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) - vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING]; + vb->reporting_vq = vqs[idx++]; return 0; }
Currently, the init_vqs function within the virtio_balloon driver relies on the condition that certain names array entries are null in order to skip the initialization of some virtual queues (vqs). This behavior is unique to this part of the codebase. In an upcoming commit, we plan to eliminate this dependency by removing the function entirely. Therefore, with this change, we are ensuring that the virtio_balloon no longer depends on the aforementioned function. Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> --- drivers/virtio/virtio_balloon.c | 41 +++++++++++++++------------------ 1 file changed, 19 insertions(+), 22 deletions(-)