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

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Date:   Mon, 15 May 2023 11:24:51 +0000
From:   "Wang, Zhi A" <zhi.a.wang@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v3 05/28] drm/i915/gvt: Explicitly check that vGPU is
 attached before shadowing

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@...gle.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) {