Re: [PATCH v3 00/10] Update vfio_pin/unpin_pages API

Alex Williamson
2022-07-23T01:09:09Z

On Fri, 22 Jul 2022 17:38:25 -0700
Nicolin Chen <nicolinc@nvidia.com> wrote:

> On Fri, Jul 22, 2022 at 06:18:00PM -0600, Alex Williamson wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > On Fri, 22 Jul 2022 16:12:19 -0700
> > Nicolin Chen <nicolinc@nvidia.com> wrote:
> >
> > > On Fri, Jul 22, 2022 at 04:11:29PM -0600, Alex Williamson wrote:
> > >
> > > > GVT-g explodes for me with this series on my Broadwell test system,
> > > > continuously spewing the following:
> > >
> > > Thank you for running additional tests.
> > >
> > > > [ 47.348778] WARNING: CPU: 3 PID: 501 at drivers/vfio/vfio_iommu_type1.c:978 vfio_iommu_type1_unpin_pages+0x7b/0x100 [vfio_iommu_type1]
> > >
> > > > Line 978 is the WARN_ON(i != npage) line. For the cases where we don't
> > > > find a matching vfio_dma, I'm seeing addresses that look maybe like
> > > > we're shifting a value that's already an iova by PAGE_SHIFT somewhere.
> > >
> > > Hmm..I don't understand the PAGE_SHIFT part. Do you mind clarifying?
> >
> > The iova was a very large address for a 4GB VM with a lot of zeros on
> > the low order bits, ex. 0x162459000000. Thanks,
>
> Ah! Thanks for the hint. The following commit did a double shifting:
> "vfio: Pass in starting IOVA to vfio_pin/unpin_pages AP"
>
> And the following change should fix:
> -------------------
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 481dd2aeb40e..4790c7f35b88 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -293,7 +293,7 @@ static int gvt_dma_map_page(struct intel_vgpu *vgpu, unsigned long gfn,
> if (dma_mapping_error(dev, *dma_addr)) {
> gvt_vgpu_err("DMA mapping failed for pfn 0x%lx, ret %d\n",
> page_to_pfn(page), ret);
> - gvt_unpin_guest_page(vgpu, gfn << PAGE_SHIFT, size);
> + gvt_unpin_guest_page(vgpu, gfn, size);
> return -ENOMEM;
> }
>
> @@ -306,7 +306,7 @@ static void gvt_dma_unmap_page(struct intel_vgpu *vgpu, unsigned long gfn,
> struct device *dev = vgpu->gvt->gt->i915->drm.dev;
>
> dma_unmap_page(dev, dma_addr, size, DMA_BIDIRECTIONAL);
> - gvt_unpin_guest_page(vgpu, gfn << PAGE_SHIFT, size);
> + gvt_unpin_guest_page(vgpu, gfn, size);
> }
>
> static struct gvt_dma *__gvt_cache_find_dma_addr(struct intel_vgpu *vgpu,
> -------------------

Looks likely. Not sure how Terrance was able to test this successfully
though.

> So, I think that I should send a v4, given that the patches aren't
> officially applied?

Yep, please rebase on current vfio next branch. Thanks,

Alex