| Message ID | 20200404094101.672954-3-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/6] amdgpu: a NULL ->mm does not mean a thread is a kthread | expand |
Hello! On 04.04.2020 12:40, Christoph Hellwig wrote: > Use the proper API instead. > > Fixes: f440c8a572d7 ("drm/i915/gvt/kvmgt: read/write GPA via KVM API") > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/gpu/drm/i915/gvt/kvmgt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c > index 074c4efb58eb..5848400620b4 100644 > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > @@ -2037,7 +2037,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa, > struct kvmgt_guest_info *info; > struct kvm *kvm; > int idx, ret; > - bool kthread = current->mm == NULL; > + bool kthread = (current->flags & PF_KTHREAD); Don't need the parens. [...] MBR, Sergei
On Sat, Apr 04, 2020 at 11:40:57AM +0200, Christoph Hellwig wrote: > Use the proper API instead. > > Fixes: f440c8a572d7 ("drm/i915/gvt/kvmgt: read/write GPA via KVM API") > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/gpu/drm/i915/gvt/kvmgt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c > index 074c4efb58eb..5848400620b4 100644 > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > @@ -2037,7 +2037,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa, > struct kvmgt_guest_info *info; > struct kvm *kvm; > int idx, ret; > - bool kthread = current->mm == NULL; > + bool kthread = (current->flags & PF_KTHREAD); > > if (!handle_valid(handle)) > return -ESRCH; > -- > 2.25.1 > hi we were removing this code. see https://lore.kernel.org/kvm/20200313031109.7989-1-yan.y.zhao@intel.com/ The implementation of vfio_dma_rw() has been in vfio next tree. https://github.com/awilliam/linux-vfio/commit/8d46c0cca5f4dc0538173d62cd36b1119b5105bc in vfio_dma_rw(), we still use bool kthread = current->mm == NULL. because if current->mm != NULL and current->flags & PF_KTHREAD, instead of calling use_mm(), we first check if (current->mm == mm) and allow copy_to_user() if it's true. Do you think it's all right? Thanks Yan > _______________________________________________ > intel-gvt-dev mailing list > intel-gvt-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
On Mon, Apr 06, 2020 at 11:08:46PM -0400, Yan Zhao wrote: > hi > we were removing this code. see > https://lore.kernel.org/kvm/20200313031109.7989-1-yan.y.zhao@intel.com/ This didn't make 5.7-rc1. > The implementation of vfio_dma_rw() has been in vfio next tree. > https://github.com/awilliam/linux-vfio/commit/8d46c0cca5f4dc0538173d62cd36b1119b5105bc This made 5.7-rc1, so I'll update the series to take it into account. T > in vfio_dma_rw(), we still use > bool kthread = current->mm == NULL. > because if current->mm != NULL and current->flags & PF_KTHREAD, instead > of calling use_mm(), we first check if (current->mm == mm) and allow copy_to_user() if it's true. > > Do you think it's all right? I can't think of another way for a kernel thread to have a mm indeed.
On Mon, Apr 13, 2020 at 03:27:30PM +0200, Christoph Hellwig wrote: > On Mon, Apr 06, 2020 at 11:08:46PM -0400, Yan Zhao wrote: > > hi > > we were removing this code. see > > https://lore.kernel.org/kvm/20200313031109.7989-1-yan.y.zhao@intel.com/ > > This didn't make 5.7-rc1. > > > The implementation of vfio_dma_rw() has been in vfio next tree. > > https://github.com/awilliam/linux-vfio/commit/8d46c0cca5f4dc0538173d62cd36b1119b5105bc > > > This made 5.7-rc1, so I'll update the series to take it into account. > > T > > in vfio_dma_rw(), we still use > > bool kthread = current->mm == NULL. > > because if current->mm != NULL and current->flags & PF_KTHREAD, instead > > of calling use_mm(), we first check if (current->mm == mm) and allow copy_to_user() if it's true. > > > > Do you think it's all right? > > I can't think of another way for a kernel thread to have a mm indeed. for example, before calling to vfio_dma_rw(), a kernel thread has already called use_mm(), then its current->mm is not null, and it has flag PF_KTHREAD. in this case, we just want to allow the copy_to_user() directly if current->mm == mm, rather than call another use_mm() again. do you think it makes sense? Thanks Yan > _______________________________________________ > intel-gvt-dev mailing list > intel-gvt-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
On Mon, Apr 13, 2020 at 08:04:10PM -0400, Yan Zhao wrote: > > I can't think of another way for a kernel thread to have a mm indeed. > for example, before calling to vfio_dma_rw(), a kernel thread has already > called use_mm(), then its current->mm is not null, and it has flag > PF_KTHREAD. > in this case, we just want to allow the copy_to_user() directly if > current->mm == mm, rather than call another use_mm() again. > > do you think it makes sense? I mean no other way than using use_mm. That being said nesting potentional use_mm callers sounds like a rather bad idea, and we should avoid that.
On Tue, Apr 14, 2020 at 09:00:13AM +0200, Christoph Hellwig wrote: > On Mon, Apr 13, 2020 at 08:04:10PM -0400, Yan Zhao wrote: > > > I can't think of another way for a kernel thread to have a mm indeed. > > for example, before calling to vfio_dma_rw(), a kernel thread has already > > called use_mm(), then its current->mm is not null, and it has flag > > PF_KTHREAD. > > in this case, we just want to allow the copy_to_user() directly if > > current->mm == mm, rather than call another use_mm() again. > > > > do you think it makes sense? > > I mean no other way than using use_mm. That being said nesting > potentional use_mm callers sounds like a rather bad idea, and we > should avoid that. yes, agree. I was explaining why we just use "current->mm == NULL" (not "current->flag & PF_KTHREAD") as a criteria to call use_mm() in vfio_dma_rw(), which you might ask us when you take that part into your series. :)
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c index 074c4efb58eb..5848400620b4 100644 --- a/drivers/gpu/drm/i915/gvt/kvmgt.c +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c @@ -2037,7 +2037,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa, struct kvmgt_guest_info *info; struct kvm *kvm; int idx, ret; - bool kthread = current->mm == NULL; + bool kthread = (current->flags & PF_KTHREAD); if (!handle_valid(handle)) return -ESRCH;
Use the proper API instead. Fixes: f440c8a572d7 ("drm/i915/gvt/kvmgt: read/write GPA via KVM API") Signed-off-by: Christoph Hellwig <hch@lst.de> --- drivers/gpu/drm/i915/gvt/kvmgt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)