Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled

[Borislav Petkov]

On Thu, Aug 20, 2020 at 07:50:50PM -0700, Sean Christopherson wrote:
> +	 * Disallow RDPID if KVM is enabled as it may consume a guest's TSC_AUX
> +	 * if an NMI arrives in KVM's run loop.  KVM loads guest's TSC_AUX on
> +	 * VM-Enter and may not restore the host's value until the CPU returns
> +	 * to userspace, i.e. KVM depends on the kernel not using TSC_AUX.
>  	 */

And frankly, this is really unfair. The kernel should be able to use any
MSR. IOW, KVM needs to be fixed here. I'm sure it context-switches other
MSRs so one more MSR is not a big deal.

-- 
Regards/Gruss,
    Boris.

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