Re: [PATCH v4 17/23] i386/cpu: Migrate MSR_IA32_PL0_SSP for FRED and CET-SHSTK

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/18/25 04:42, Zhao Liu wrote:
> From: "Xin Li (Intel)" <xin@zytor.com>
> 
> Both FRED and CET-SHSTK need MSR_IA32_PL0_SSP, so add the vmstate for
> this MSR.
> 
> When CET-SHSTK is not supported, MSR_IA32_PL0_SSP keeps accessible, but
> its value doesn't take effect. Therefore, treat this vmstate as a
> subsection rather than a fix for the previous FRED vmstate.
> 
> Tested-by: Farrah Chen <farrah.chen@intel.com>
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> Co-developed-by: Zhao Liu <zhao1.liu@intel.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Changes Since v3:
>   - New commit.
> ---
>   target/i386/machine.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 45b7cea80aa7..0a756573b6cd 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -1668,6 +1668,31 @@ static const VMStateDescription vmstate_triple_fault = {
>       }
>   };
>   
> +static bool pl0_ssp_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +#ifdef TARGET_X86_64
> +    if (env->features[FEAT_7_1_EAX] & CPUID_7_1_EAX_FRED) {
> +        return true;
> +    }
> +#endif
> +
> +    return !!(env->features[FEAT_7_0_ECX] & CPUID_7_0_ECX_CET_SHSTK);

Can you just make it return "!!(env->pl0_ssp)"?  If all of these bits 
are zero the MSR will not be settable, and this way you can migrate VMs 
as long as they don't use PL0_SSP.

Paolo