linux-kernel - Re: [RFC PATCH v3 12/21] KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc

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Message-ID: <e62157f2-d691-4cf1-8cb0-717580b8a836@xen.org>
Date: Fri, 24 May 2024 14:56:53 +0100
From: Paul Durrant <xadimgnik@...il.com>
To: David Woodhouse <dwmw2@...radead.org>, kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
 Sean Christopherson <seanjc@...gle.com>, 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>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira
 <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>,
 Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, jalliste@...zon.co.uk, sveith@...zon.de,
 zide.chen@...el.com, Dongli Zhang <dongli.zhang@...cle.com>,
 Chenyi Qiang <chenyi.qiang@...el.com>
Subject: Re: [RFC PATCH v3 12/21] KVM: x86: Remove implicit rdtsc() from
 kvm_compute_l1_tsc_offset()

On 22/05/2024 01:17, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> Let the callers pass the host TSC value in as an explicit parameter.
> 
> This leaves some fairly obviously stupid code, which using this function
> to compare the guest TSC at some *other* time, with the newly-minted TSC
> value from rdtsc(). Unless it's being used to measure *elapsed* time,
> that isn't very sensible.
> 
> In this case, "obviously stupid" is an improvement over being non-obviously
> so.
> 
> No functional change intended.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> ---
>   arch/x86/kvm/x86.c | 14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
> 

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