Re: [Intel-gfx] [PATCH v3 05/28] drm/i915/gvt: Explicitly check that vGPU is attached before shadowing

Wang, Zhi A
2023-05-15T11:24:58Z

On 5/13/2023 8:35 AM, Sean Christopherson wrote:
> Move the check that a vGPU is attacked from is_2MB_gtt_possible() to its
> sole caller, ppgtt_populate_shadow_entry(). All of the paths in
> ppgtt_populate_shadow_entry() eventually check for attachment by way of
> intel_gvt_dma_map_guest_page(), but explicitly checking can avoid
> unnecessary work and will make it more obvious that a future cleanup of
> is_2MB_gtt_possible() isn't introducing a bug.
>

It might be better move this check to shadow_ppgtt_mm() which is used
in both shadow page table creation and pinning path so that the path
can bail out even earlier when creating a shadow page table but a vGPU
has not been attached to KVM yet.

> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> drivers/gpu/drm/i915/gvt/gtt.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 5426a27c1b71..2aed31b497c9 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -1163,8 +1163,6 @@ static int is_2MB_gtt_possible(struct intel_vgpu *vgpu,
> if (!HAS_PAGE_SIZES(vgpu->gvt->gt->i915, I915_GTT_PAGE_SIZE_2M))
> return 0;
>
> - if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, vgpu->status))
> - return -EINVAL;
> pfn = gfn_to_pfn(vgpu->vfio_device.kvm, ops->get_pfn(entry));
> if (is_error_noslot_pfn(pfn))
> return -EINVAL;
> @@ -1277,6 +1275,9 @@ static int ppgtt_populate_shadow_entry(struct intel_vgpu *vgpu,
> if (!pte_ops->test_present(ge))
> return 0;
>
> + if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, vgpu->status))
> + return -EINVAL;
> +
> gfn = pte_ops->get_pfn(ge);
>
> switch (ge->type) {