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From: Paul Durrant <xadimgnik@gmail.com>
Message-ID: <b668e938-a48f-4295-a9ec-e66f0abd1bb0@xen.org>
Date: Fri, 19 Apr 2024 16:53:49 +0100
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Subject: Re: [PATCH 07/10] KVM: x86: Avoid NTP frequency skew for KVM clock on
 32-bit host
To: David Woodhouse <dwmw2@infradead.org>, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
 Sean Christopherson <seanjc@google.com>, Thomas Gleixner
 <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
 Shuah Khan <shuah@kernel.org>, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
 Oliver Upton <oliver.upton@linux.dev>, Marcelo Tosatti
 <mtosatti@redhat.com>, jalliste@amazon.co.uk, sveith@amazon.de
References: <20240418193528.41780-1-dwmw2@infradead.org>
 <20240418193528.41780-8-dwmw2@infradead.org>
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On 18/04/2024 20:34, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> Commit 53fafdbb8b21 ("KVM: x86: switch KVMCLOCK base to monotonic raw
> clock") did so only for 64-bit hosts, by capturing the boot offset from
> within the existing clocksource notifier update_pvclock_gtod().
> 
> That notifier was added in commit 16e8d74d2da9 ("KVM: x86: notifier for
> clocksource changes") but only on x86_64, because its original purpose
> was just to disable the "master clock" mode which is only supported on
> x86_64.
> 
> Now that the notifier is used for more than disabling master clock mode,
> (well, OK, more than a decade later but clocks are hard), enable it for
> the 32-bit build too so that get_kvmclock_base_ns() can be unaffected by
> NTP sync on 32-bit too.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   arch/x86/kvm/x86.c | 18 ++++++------------
>   1 file changed, 6 insertions(+), 12 deletions(-)
> 

Reviewed-by: Paul Durrant <paul@xen.org>