linux-kernel - Re: [PATCH v5] KVM x86/xen: add an override for PVCLOCK_TSC_STABLE

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Message-ID: <b28dc7d2-a83d-4e0e-8a01-524baeb23151@xen.org>
Date:   Thu, 30 Nov 2023 15:49:07 +0000
From:   Paul Durrant <xadimgnik@...il.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        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,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v5] KVM x86/xen: add an override for
 PVCLOCK_TSC_STABLE_BIT

On 08/11/2023 18:39, David Woodhouse wrote:
> On Thu, 2023-11-02 at 16:21 +0000, Paul Durrant wrote:
>> From: Paul Durrant <pdurrant@...zon.com>
>>
>> Unless explicitly told to do so (by passing 'clocksource=tsc' and
>> 'tsc=stable:socket', and then jumping through some hoops concerning
>> potential CPU hotplug) Xen will never use TSC as its clocksource.
>> Hence, by default, a Xen guest will not see PVCLOCK_TSC_STABLE_BIT set
>> in either the primary or secondary pvclock memory areas. This has
>> led to bugs in some guest kernels which only become evident if
>> PVCLOCK_TSC_STABLE_BIT *is* set in the pvclocks. Hence, to support
>> such guests, give the VMM a new Xen HVM config flag to tell KVM to
>> forcibly clear the bit in the Xen pvclocks.
>>
>> Signed-off-by: Paul Durrant <pdurrant@...zon.com>
> 
> Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>

Sean,

   Is any more work needed on this?

   Paul