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

[Yan Zhao]

hi Sean

Do you think it's necessary to double check that struct page pointers
are also contiguous?

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;
 }

BTW, I've sent a separate fix for vfio_iommu_type1_pin_pages() to ensure
struct page is a valid address.
https://lore.kernel.org/lkml/20230516093007.15234-1-yan.y.zhao@xxxxxxxxx/

On Fri, May 12, 2023 at 05:35:35PM -0700, Sean Christopherson wrote:
> When shadowing a GTT entry with a 2M page, verify that the pfns are
> contiguous, not just that the struct page pointers are contiguous.  The
> memory map is virtual contiguous if "CONFIG_FLATMEM=y ||
> CONFIG_SPARSEMEM_VMEMMAP=y", but not for "CONFIG_SPARSEMEM=y &&
> CONFIG_SPARSEMEM_VMEMMAP=n", so theoretically KVMGT could encounter struct
> pages that are virtually contiguous, but not physically contiguous.
> 
> In practice, this flaw is likely a non-issue as it would cause functional
> problems iff a section isn't 2M aligned _and_ is directly adjacent to
> another section with discontiguous pfns.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  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 de675d799c7d..429f0f993a13 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -161,7 +161,7 @@ static int gvt_pin_guest_page(struct intel_vgpu *vgpu, unsigned long gfn,
>  
>  		if (npage == 0)
>  			base_page = cur_page;
> -		else if (base_page + npage != cur_page) {
> +		else if (page_to_pfn(base_page) + npage != page_to_pfn(cur_page)) {
>  			gvt_vgpu_err("The pages are not continuous\n");
>  			ret = -EINVAL;
>  			npage++;
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>