linux-kernel - Re: [PATCH v4 03/29] drm/i915/gvt: Verify hugepages are contiguous in physical address space

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Date:   Tue, 1 Aug 2023 09:47:17 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.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>,
        Yongwei Ma <yongwei.ma@...el.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v4 03/29] drm/i915/gvt: Verify hugepages are contiguous
 in physical address space

Reviewed-by: Yan Zhao <yan.y.zhao@...el.com>

On Fri, Jul 28, 2023 at 06:35:09PM -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.
> 
> Tested-by: Yongwei Ma <yongwei.ma@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  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++;
> -- 
> 2.41.0.487.g6d72f3e995-goog
>