linux-kernel - Re: [PATCH] x86/sev: Improve handling of writes to intercepted GUEST_TSC

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Message-ID: <85ecuhx1eh.fsf@amd.com>
Date: Tue, 15 Jul 2025 09:13:10 +0000
From: Nikunj A Dadhania <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>, Sean Christopherson <seanjc@...gle.com>
CC: Tom Lendacky <thomas.lendacky@....com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<dave.hansen@...ux.intel.com>, <santosh.shukla@....com>
Subject: Re: [PATCH] x86/sev: Improve handling of writes to intercepted
 GUEST_TSC_FREQ

Borislav Petkov <bp@...en8.de> writes:

> On Mon, Jul 14, 2025 at 09:36:04AM -0700, Sean Christopherson wrote:
>> Or as Tom suggested, return ES_EXCEPTION and let the kernel's normal machinery
>> WARN on the bad WRMSR.
>
> Ack.

That will panic the SNP guest instead of #GP:

root@...ntu:~# wrmsr 0xc0010134 0
[   20.804335] ------------[ cut here ]------------
[   20.804336] WARNING: arch/x86/coco/sev/vc-handle.c:383 at vc_handle_exitcode.part.0+0xc1b/0x1090, CPU#0: wrmsr/607
...
[   20.804507] SEV: Unsupported exception in #VC instruction emulation - can't continue
[   20.804508] ------------[ cut here ]------------
[   20.804508] kernel BUG at arch/x86/coco/sev/vc-handle.c:123!
[   20.804514] Oops: invalid opcode: 0000 [#1] SMP NOPTI

Regards,
Nikunj