Re: [PATCH v12 17/19] x86/kvmclock: Abort SecureTSC enabled guest when kvmclock is selected

[Tom Lendacky]

On 10/9/24 04:28, Nikunj A Dadhania wrote:
> SecureTSC enabled guests should use TSC as the only clock source, abort
> the guest when clock source switches to hypervisor controlled kvmclock.
> 
> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> ---
>  arch/x86/kernel/kvmclock.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index 5cd3717e103b..552c28cda874 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -22,6 +22,7 @@
>  #include <asm/x86_init.h>
>  #include <asm/kvmclock.h>
>  #include <asm/timer.h>
> +#include <asm/sev.h>
>  
>  static int kvmclock __initdata = 1;
>  static int kvmclock_vsyscall __initdata = 1;
> @@ -155,6 +156,13 @@ static void enable_kvm_sc_work(struct work_struct *work)
>  {
>  	u8 flags;
>  
> +	/*
> +	 * For guest with SecureTSC enabled, TSC should be the only clock source.

s/For guest/For a guest/
s/TSC should/The TSC should/

> +	 * Abort the guest when kvmclock is selected as the clock source.
> +	 */
> +	if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
> +		snp_abort();

Can a message be issued here?

Also, you could use sev_es_terminate() to provide a specific Linux
reason code, e.g.:

  sev_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECURE_TSC_KVMCLOCK);

or whatever name you want to use for this situation.

Thanks,
Tom

> +
>  	old_pv_sched_clock = static_call_query(pv_sched_clock);
>  	flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
>  	kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);