| Message ID | 20190606202831.44135-6-farman@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | s390: vfio-ccw code rework | expand |
On Thu, 6 Jun 2019 22:28:27 +0200 Eric Farman <farman@linux.ibm.com> wrote: > While processing a channel program, we currently have two nested > arrays that carry a slightly different structure. The direct CCW > path creates this: > > ccwchain->pfn_array_table[1]->pfn_array[#pages] > > while an IDA CCW creates: > > ccwchain->pfn_array_table[#idaws]->pfn_array[1] > > The distinction appears to state that each pfn_array_table entry > points to an array of contiguous pages, represented by a pfn_array, > um, array. Since the direct-addressed scenario can ONLY represent > contiguous pages, it makes the intermediate array necessary but > difficult to recognize. Meanwhile, since an IDAL can contain > non-contiguous pages and there is no logic in vfio-ccw to detect > adjacent IDAWs, it is the second array that is necessary but appearing > to be superfluous. > > I am not aware of any documentation that states the pfn_array[] needs > to be of contiguous pages; it is just what the code does today. > I don't see any reason for this either, let's just flip the IDA > codepath around so that it generates: > > ch_pat->pfn_array_table[1]->pfn_array[#idaws] > > This will bring it in line with the direct-addressed codepath, > so that we can understand the behavior of this memory regardless > of what type of CCW is being processed. And it means the casual > observer does not need to know/care whether the pfn_array[] > represents contiguous pages or not. > > NB: The existing vfio-ccw code only supports 4K-block Format-2 IDAs, > so that "#pages" == "#idaws" in this area. This means that we will > have difficulty with this overlap in terminology if support for > Format-1 or 2K-block Format-2 IDAs is ever added. I don't think that > this patch changes our ability to make that distinction. I agree; and knowing that later patches will simplify things further, I think it will even be easier to do than on the current code base. > > Signed-off-by: Eric Farman <farman@linux.ibm.com> > --- > drivers/s390/cio/vfio_ccw_cp.c | 26 +++++++++++--------------- > 1 file changed, 11 insertions(+), 15 deletions(-) Reviewed-by: Cornelia Huck <cohuck@redhat.com>
diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c index 5b98bea433b7..86a0e76ef2b5 100644 --- a/drivers/s390/cio/vfio_ccw_cp.c +++ b/drivers/s390/cio/vfio_ccw_cp.c @@ -635,7 +635,6 @@ static int ccwchain_fetch_idal(struct ccwchain *chain, { struct ccw1 *ccw; struct pfn_array_table *pat; - struct pfn_array *pa; unsigned long *idaws; u64 idaw_iova; unsigned int idaw_nr, idaw_len; @@ -656,10 +655,14 @@ static int ccwchain_fetch_idal(struct ccwchain *chain, /* Pin data page(s) in memory. */ pat = chain->ch_pat + idx; - ret = pfn_array_table_init(pat, idaw_nr); + ret = pfn_array_table_init(pat, 1); if (ret) goto out_init; + ret = pfn_array_alloc(pat->pat_pa, idaw_iova, bytes); + if (ret) + goto out_unpin; + /* Translate idal ccw to use new allocated idaws. */ idaws = kzalloc(idaw_len, GFP_DMA | GFP_KERNEL); if (!idaws) { @@ -673,22 +676,15 @@ static int ccwchain_fetch_idal(struct ccwchain *chain, ccw->cda = virt_to_phys(idaws); - for (i = 0; i < idaw_nr; i++) { - idaw_iova = *(idaws + i); - pa = pat->pat_pa + i; - - ret = pfn_array_alloc(pa, idaw_iova, 1); - if (ret < 0) - goto out_free_idaws; - - if (!ccw_does_data_transfer(ccw)) { - pa->pa_nr = 0; - continue; - } + for (i = 0; i < idaw_nr; i++) + pat->pat_pa->pa_iova_pfn[i] = idaws[i] >> PAGE_SHIFT; - ret = pfn_array_pin(pa, cp->mdev); + if (ccw_does_data_transfer(ccw)) { + ret = pfn_array_pin(pat->pat_pa, cp->mdev); if (ret < 0) goto out_free_idaws; + } else { + pat->pat_pa->pa_nr = 0; } pfn_array_table_idal_create_words(pat, idaws);
While processing a channel program, we currently have two nested arrays that carry a slightly different structure. The direct CCW path creates this: ccwchain->pfn_array_table[1]->pfn_array[#pages] while an IDA CCW creates: ccwchain->pfn_array_table[#idaws]->pfn_array[1] The distinction appears to state that each pfn_array_table entry points to an array of contiguous pages, represented by a pfn_array, um, array. Since the direct-addressed scenario can ONLY represent contiguous pages, it makes the intermediate array necessary but difficult to recognize. Meanwhile, since an IDAL can contain non-contiguous pages and there is no logic in vfio-ccw to detect adjacent IDAWs, it is the second array that is necessary but appearing to be superfluous. I am not aware of any documentation that states the pfn_array[] needs to be of contiguous pages; it is just what the code does today. I don't see any reason for this either, let's just flip the IDA codepath around so that it generates: ch_pat->pfn_array_table[1]->pfn_array[#idaws] This will bring it in line with the direct-addressed codepath, so that we can understand the behavior of this memory regardless of what type of CCW is being processed. And it means the casual observer does not need to know/care whether the pfn_array[] represents contiguous pages or not. NB: The existing vfio-ccw code only supports 4K-block Format-2 IDAs, so that "#pages" == "#idaws" in this area. This means that we will have difficulty with this overlap in terminology if support for Format-1 or 2K-block Format-2 IDAs is ever added. I don't think that this patch changes our ability to make that distinction. Signed-off-by: Eric Farman <farman@linux.ibm.com> --- drivers/s390/cio/vfio_ccw_cp.c | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-)