linux-kernel - Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic

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Date:   Thu, 12 May 2022 21:27:22 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused
 cmpxchg to be not atomic

On Thu, May 12, 2022, Paolo Bonzini wrote:
> On 5/12/22 12:14, Maxim Levitsky wrote:
> > Yes, this is the root cause of the TDP mmu leak I was doing debug of in the last week.
> > Non working cmpxchg on which TDP mmu relies makes it install two differnt shadow pages
> > under same spte.
> 
> Awesome!  And queued, thanks.

If you haven't done so already, can you add 

  Cc: stable@...r.kernel.org

Also, given that we have concrete proof that not honoring atomic accesses can have
dire consequences for the guest, what about adding a capability to turn the emul_write
path into an emulation error?