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

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Date:   Tue, 6 Apr 2021 21:06:50 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
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 Tue, Apr 06, 2021 at 08:35:55PM +0200, Paolo Bonzini wrote:
> 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.

Ah, ok, thanks, got confused there.

greg k-h