linux-kernel - Re: [PATCH v15 12/13] x86/kvmclock: Abort SecureTSC enabled guest when kvmclock is selected

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Message-ID: <09187d10-78b3-402f-be77-138cea98d8b7@amd.com>
Date: Thu, 2 Jan 2025 11:04:21 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [PATCH v15 12/13] x86/kvmclock: Abort SecureTSC enabled guest
 when kvmclock is selected

On 1/1/2025 9:49 PM, Borislav Petkov wrote:
> On Wed, Jan 01, 2025 at 03:14:12PM +0530, Nikunj A. Dadhania wrote:
>> I can drop this patch, and if the admin wants to change the clock 
>> source to kvm-clock from Secure TSC, that will be permitted.
> 
> Why would the admin want that and why would we even support that?

I am not saying that admin will do that, I am saying that it is a possibility.

Changing clocksource is supported via sysfs interface:

echo "kvm-clock" > /sys/devices/system/clocksource/clocksource0/current_clocksource

This is what we are trying to prevent in this patch.

Regards,
Nikunj