linux-kernel - Re: [PATCH 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled

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Date:   Wed, 11 Oct 2023 16:11:03 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     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,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/13] x86/kvm: Do not try to disable kvmclock if it was
 not enabled

On Tue, Oct 10, 2023 at 06:53:27AM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> On 10/5/2023 6:13 AM, Kirill A. Shutemov wrote:
> > kvm_guest_cpu_offline() tries to disable kvmclock regardless if it is
> > present in the VM. It leads to write to a MSR that doesn't exist on some
> > configurations, namely in TDX guest:
> > 
> > 	unchecked MSR access error: WRMSR to 0x12 (tried to write 0x0000000000000000)
> > 	at rIP: 0xffffffff8110687c (kvmclock_disable+0x1c/0x30)
> > 
> > kvmclock enabling is gated by CLOCKSOURCE and CLOCKSOURCE2 KVM paravirt
> > features.
> > 
> > Do not disable kvmclock if it was not enumerated or disabled by user
> > from kernel command line.
> 
> For the above warning,  check for CLOCKSOURCE and CLOCKSOURCE2
> feature is sufficient, right? Do we need to include user/command-line
> disable check here?

The command line disables kvmclock, even if it is enumerated, so disabling
it is not needed.

Anyway, I reworked the patch already based on Sean's feedback. No need in
taking parameter into account directly now.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov