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

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Message-ID: <ZGTpsvZed+r3Low1@google.com>
Date:   Wed, 17 May 2023 07:50:26 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v3 03/28] drm/i915/gvt: Verify hugepages are contiguous in
 physical address space

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.

> 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 again!