linux-kernel - Re: [PATCH v2] KVM x86/xen: add an override for PVCLOCK_TSC_STABLE

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Date:   Wed, 1 Nov 2023 11:02:16 +0000
From:   Paul Durrant <xadimgnik@...il.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM x86/xen: add an override for
 PVCLOCK_TSC_STABLE_BIT

On 31/10/2023 22:48, David Woodhouse wrote:
> On Tue, 2023-10-31 at 15:39 -0700, Sean Christopherson wrote:
>> On Tue, Oct 31, 2023, Paul Durrant wrote:
>>>
>>> +       if (force_tsc_unstable)
>>> +               guest_hv_clock->flags &= ~PVCLOCK_TSC_STABLE_BIT;
>>
>> I don't see how this works.  This clears the bit in the guest copy, then clobbers
>> all of guest_hv_clock with a memcpy().
> 
> Agreed, that seems wrong.
> 

It is indeed. Looks like it got moved the wrong side of the memcpy() 
when I rebased.

   Paul