linux-kernel - Re: [PATCHv4 05/14] x86/kvm: Do not try to disable kvmclock if it was not enabled

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Date:   Tue, 12 Dec 2023 02:10:35 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.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>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.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>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        "Huang, Kai" <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
        kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCHv4 05/14] x86/kvm: Do not try to disable kvmclock if it
 was not enabled

On Tue, Dec 05, 2023 at 03:45:01AM +0300, 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 enabled.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Fixes: c02027b5742b ("x86/kvm: Disable kvmclock on all CPUs on shutdown")
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Wanpeng Li <wanpengli@...cent.com>

Paolo, Sean, any chance you can get it in through KVM tree while the rest
of kexec patchset is pending? The problem is visible on normal reboot too.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov