linux-kernel - Re: [PATCH] KVM: MMU: protect TDP MMU pages only down to required level

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Date:   Wed, 7 Apr 2021 09:31:59 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH] KVM: MMU: protect TDP MMU pages only down to required
 level



On 2021/4/7 7:38, Sean Christopherson wrote:
> On Tue, Apr 06, 2021, Keqian Zhu wrote:
>> Hi Paolo,
>>
>> I'm just going to fix this issue, and found that you have done this ;-)
> 
> Ha, and meanwhile I'm having a serious case of deja vu[1].  It even received a
> variant of the magic "Queued, thanks"[2].  Doesn't appear in either of the 5.12
> pull requests though, must have gotten lost along the way.
Good job. We should pick them up :)

> 
> [1] https://lkml.kernel.org/r/20210213005015.1651772-3-seanjc@google.com
> [2] https://lkml.kernel.org/r/b5ab72f2-970f-64bd-891c-48f1c303548d@redhat.com
> 
>> Please feel free to add:
>>
>> Reviewed-by: Keqian Zhu <zhukeqian1@...wei.com>
>>
>> Thanks,
>> Keqian
>>
>> On 2021/4/2 20:17, Paolo Bonzini wrote:
>>> When using manual protection of dirty pages, it is not necessary
>>> to protect nested page tables down to the 4K level; instead KVM
>>> can protect only hugepages in order to split them lazily, and
>>> delay write protection at 4K-granularity until KVM_CLEAR_DIRTY_LOG.
>>> This was overlooked in the TDP MMU, so do it there as well.
>>>
>>> Fixes: a6a0b05da9f37 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
>>> Cc: Ben Gardon <bgardon@...gle.com>
>>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>> ---
>>>  arch/x86/kvm/mmu/mmu.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>>> index efb41f31e80a..0d92a269c5fa 100644
>>> --- a/arch/x86/kvm/mmu/mmu.c
>>> +++ b/arch/x86/kvm/mmu/mmu.c
>>> @@ -5538,7 +5538,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>>>  	flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
>>>  				start_level, KVM_MAX_HUGEPAGE_LEVEL, false);
>>>  	if (is_tdp_mmu_enabled(kvm))
>>> -		flush |= kvm_tdp_mmu_wrprot_slot(kvm, memslot, PG_LEVEL_4K);
>>> +		flush |= kvm_tdp_mmu_wrprot_slot(kvm, memslot, start_level);
>>>  	write_unlock(&kvm->mmu_lock);
>>>  
>>>  	/*
>>>
> .
>