Re: [Intel-gfx] [PATCH v3 03/28] drm/i915/gvt: Verify hugepages are contiguous in physical address space

Yan Zhao
2023-05-18T09:32:04Z

On Wed, May 17, 2023 at 07:50:26AM -0700, Sean Christopherson wrote:
> On Tue, May 16, 2023, Yan Zhao wrote:
> > hi Sean
> >
> > Do you think it's necessary to double check that struct page pointers
> > are also contiguous?
>
> No, the virtual address space should be irrelevant. The only way it would be
> problematic is if something in dma_map_page() expected to be able to access the
> entire chunk of memory by getting the virtual address of only the first page,
> but I can't imagine that code is reading or writing memory, let alone doing so
> across a huge range of memory.
Yes, I do find arm_iommu version of dma_map_page() access the memory by getting
virtual address of pages passed in, but it's implemented as page by page, not only
from the first page.

dma_map_page
dma_map_page_attrs
ops->map_page
arm_iommu_map_page
__dma_page_cpu_to_dev
dma_cache_maint_page

Just a little worried about the condition of PFNs are contiguous
while they belong to different backends, e.g. one from system memory and
one from MMIO.
But I don't know how to avoid this without complicated checks.
And this condition might not happen in practice.

>
> > And do you like to also include a fix as below, which is to remove the
> > warning in vfio_device_container_unpin_pages() when npage is 0?
> >
> > @ -169,7 +173,8 @@ static int gvt_pin_guest_page(struct intel_vgpu *vgpu, unsigned long gfn,
> > *page = base_page;
> > return 0;
> > err:
> > - gvt_unpin_guest_page(vgpu, gfn, npage * PAGE_SIZE);
> > + if (npage)
> > + gvt_unpin_guest_page(vgpu, gfn, npage * PAGE_SIZE);
> > return ret;
> > }
>
> Sure. Want to give your SoB? I'll write a changelog.
>
Thanks!
It's just a small code piece. Whatever is convenient for you :)