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

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Message-ID: <e61ab0eb-816d-dc5d-dde5-e305a27705b2@amd.com>
Date: Tue, 15 Jul 2025 07:47:12 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Nikunj A Dadhania <nikunj@....com>, Borislav Petkov <bp@...en8.de>,
 Sean Christopherson <seanjc@...gle.com>
Cc: 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

On 7/15/25 04:13, Nikunj A Dadhania wrote:
> 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

Did you fill in the context with the #GP, i.e., ctxt->fi.vector and
ctxt->fi.error_code?

Thanks,
Tom

> 
> Regards,
> Nikunj