linux-kernel - Re: [PATCH] KVM: x86/mmu: preserve pending TLB flush across calls to kvm_tdp_mmu_zap

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Message-ID: <d93cb5c8-e54a-6f5a-c660-9d044ff2c743@redhat.com>
Date:   Tue, 6 Apr 2021 20:35:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: preserve pending TLB flush across calls to
 kvm_tdp_mmu_zap_sp

On 06/04/21 20:25, Greg KH wrote:
> On Tue, Apr 06, 2021 at 12:25:50PM -0400, Paolo Bonzini wrote:
>> Right now, if a call to kvm_tdp_mmu_zap_sp returns false, the caller
>> will skip the TLB flush, which is wrong.  There are two ways to fix
>> it:
>>
>> - since kvm_tdp_mmu_zap_sp will not yield and therefore will not flush
>>    the TLB itself, we could change the call to kvm_tdp_mmu_zap_sp to
>>    use "flush |= ..."
>>
>> - or we can chain the flush argument through kvm_tdp_mmu_zap_sp down
>>    to __kvm_tdp_mmu_zap_gfn_range.
>>
>> This patch does the former to simplify application to stable kernels.
>>
>> Cc: seanjc@...gle.com
>> Fixes: 048f49809c526 ("KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping")
>> Cc: <stable@...r.kernel.org> # 5.10.x: 048f49809c: KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping
>> Cc: <stable@...r.kernel.org> # 5.10.x: 33a3164161: KVM: x86/mmu: Don't allow TDP MMU to yield when recovering NX pages
>> Cc: <stable@...r.kernel.org>
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>> ---
>>   arch/x86/kvm/mmu/mmu.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Is this for only the stable kernels, or is it addressed toward upstream
> merges?
> 
> Confused,

It's for upstream.  I'll include it (with the expected "[ Upstream 
commit abcd ]" header) when I post the complete backport.  I'll send 
this patch to Linus as soon as I get a review even if I don't have 
anything else in the queue, so (as a general idea) the full backport 
should be sent and tested on Thursday-Friday.

Paolo