Re: [PATCH 3/3] x86: Support booting under Secure Startup via SKINIT

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.01.2021 00:10, Andrew Cooper wrote:
> --- a/xen/arch/x86/cpu/common.c
> +++ b/xen/arch/x86/cpu/common.c
> @@ -834,6 +834,29 @@ void load_system_tables(void)
>       BUG_ON(system_state != SYS_STATE_early_boot && (stack_bottom & 0xf));
>  }
>  
> +static void skinit_enable_intr(void)
> +{
> +     uint64_t val;
> +
> +     /*
> +      * If the platform is performing a Secure Launch via SKINIT
> +      * INIT_REDIRECTION flag will be active.
> +      */
> +     if ( !cpu_has_skinit || rdmsr_safe(MSR_K8_VM_CR, val) ||
> +          !(val & VM_CR_INIT_REDIRECTION) )
> +             return;
> +
> +     ap_boot_method = AP_BOOT_SKINIT;
> +
> +     /*
> +      * We don't yet handle #SX.  Disable INIT_REDIRECTION first, before
> +      * enabling GIF, so a pending INIT resets us, rather than causing a
> +      * panic due to an unknown exception.
> +      */
> +     wrmsr_safe(MSR_K8_VM_CR, val & ~VM_CR_INIT_REDIRECTION);

Why wrmsr_safe() without checking its return value? If the write
faults, we're hosed anyway, aren't we, so we may as well crash on
the offending WRMSR rather than some time later?

Jan