linux-kernel - Re: [PATCH v9 6/6] KVM: x86/mmu: Handle non-refcounted pages

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Message-ID: <9771886a-d60d-b273-9f0c-ba663acb1db8@collabora.com>
Date:   Sat, 30 Sep 2023 16:34:57 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     David Stevens <stevensd@...omium.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v9 6/6] KVM: x86/mmu: Handle non-refcounted pages

On 9/19/23 05:25, David Stevens wrote:
> On Mon, Sep 18, 2023 at 6:53 PM Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:
>>
>> On 9/11/23 05:16, David Stevens wrote:
>>> --- a/arch/x86/kvm/mmu/paging_tmpl.h
>>> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
>>> @@ -848,7 +848,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>>>  
>>>  out_unlock:
>>>       write_unlock(&vcpu->kvm->mmu_lock);
>>> -     kvm_release_pfn_clean(fault->pfn);
>>> +     if (fault->is_refcounted_page)
>>> +             kvm_set_page_accessed(pfn_to_page(fault->pfn));
>>
>> The other similar occurrences in the code that replaced
>> kvm_release_pfn_clean() with kvm_set_page_accessed() did it under the
>> held mmu_lock.
>>
>> Does kvm_set_page_accessed() needs to be invoked under the lock?
> 
> It looks like I made a mistake when folding the v8->v9 delta into the stack of
> patches to get a clean v9 series. v8 of the series returned pfns without
> reference counts from __kvm_follow_pfn, so the x86 MMU needed to mark the pages
> as accessed under the lock. v9 instead returns pfns with a refcount (i.e. does
> the same thing as __gfn_to_pfn_memslot), so the x86 MMU should instead call
> kvm_release_page_clean outside of the lock. I've included the corrected version
> of this patch in this email.
[snip]

I tested this series + the corrected version of the patch on Intel TGL using virgl/venus/virtio-intel on both qemu and crosvm on top of the recent linux-next. All is working good. Feel free to add my t-b to the v10:

Tested-by: Dmitry Osipenko <dmitry.osipenko@...labora.com> # virgl+venus+virtio-intel+i915

-- 
Best regards,
Dmitry