[RFC PATCH v3 09/29] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest

[Eric Auger]

Hi Reiji,

On 11/17/21 7:43 AM, Reiji Watanabe wrote:
> When ID_AA64DFR0_EL1.PMUVER or ID_DFR0_EL1.PERFMON is 0xf, which
> means IMPLEMENTATION DEFINED PMU supported, KVM unconditionally
> expose the value for the guest as it is.  Since KVM doesn't support
> IMPLEMENTATION DEFINED PMU for the guest, in that case KVM should
> exopse 0x0 (PMU is not implemented) instead.
s/exopse/expose
> 
> Change cpuid_feature_cap_perfmon_field() to update the field value
> to 0x0 when it is 0xf.
is it wrong to expose the guest with a Perfmon value of 0xF? Then the
guest should not use it as a PMUv3?

Eric
> 
> Fixes: 8e35aa642ee4 ("arm64: cpufeature: Extract capped perfmon fields")
> Signed-off-by: Reiji Watanabe <reijiw at google.com>
> ---
>  arch/arm64/include/asm/cpufeature.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index ef6be92b1921..fd7ad8193827 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -553,7 +553,7 @@ cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap)
>  
>  	/* Treat IMPLEMENTATION DEFINED functionality as unimplemented */
>  	if (val == ID_AA64DFR0_PMUVER_IMP_DEF)
> -		val = 0;
> +		return (features & ~mask);
>  
>  	if (val > cap) {
>  		features &= ~mask;
>