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 14:22:50 +0300
From:   "Wang, Zhi A" <zhi.a.wang@...el.com>
To:     Yan Zhao <yan.y.zhao@...el.com>,
        Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.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

On 8/1/2023 4:47 AM, Yan Zhao wrote:
> 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
>>
Reviewed-by: Zhi Wang <zhi.a.wang@...el.com>