On Wed, May 21, 2025 at 09:49:48AM -0700, Sean Christopherson wrote:
>On Mon, May 12, 2025, Chao Gao wrote:
>> @@ -772,6 +776,21 @@ static void __init fpu__init_disable_system_xstate(unsigned int legacy_size)
>> fpstate_reset(x86_task_fpu(current));
>> }
>>
>> +static void __init init_default_features(u64 kernel_max_features, u64 user_max_features)
>> +{
>> + u64 kfeatures = kernel_max_features;
>> + u64 ufeatures = user_max_features;
>> +
>> + /* Default feature sets should not include dynamic xfeatures. */
>> + kfeatures &= ~XFEATURE_MASK_USER_DYNAMIC;
>> + ufeatures &= ~XFEATURE_MASK_USER_DYNAMIC;
>> +
>> + fpu_kernel_cfg.default_features = kfeatures;
>> + fpu_user_cfg.default_features = ufeatures;
>> +
>> + guest_default_cfg.features = kfeatures;
>> +}
>> +
>> /*
>> * Enable and initialize the xsave feature.
>> * Called once per system bootup.
>> @@ -854,12 +873,8 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
>> fpu_user_cfg.max_features = fpu_kernel_cfg.max_features;
>> fpu_user_cfg.max_features &= XFEATURE_MASK_USER_SUPPORTED;
>>
>> - /* Clean out dynamic features from default */
>> - fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
>> - fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>> -
>> - fpu_user_cfg.default_features = fpu_user_cfg.max_features;
>> - fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>> + /* Now, given maximum feature set, determine default values */
>> + init_default_features(fpu_kernel_cfg.max_features, fpu_user_cfg.max_features);
>
>Passing in max_features is rather odd. I assume the intent is to capture the
>dependencies, but that falls apart by the end of series as the guest features
>are initialized as:
>
> guest_default_cfg.features = kfeatures | xfeatures_mask_guest_supervisor();
>
>where xfeatures_mask_guest_supervisor() sneakily consumes fpu_kernel_cfg.max_features,
>the very field this patch deliberately avoids consuming directly.
>
> static inline u64 xfeatures_mask_guest_supervisor(void)
> {
> return fpu_kernel_cfg.max_features & XFEATURE_MASK_GUEST_SUPERVISOR;
> }
>
Indeed, it is odd. And your suggestion looks good to me. Thanks.
I will fix this and the comment issue you pointed out and post a new version.
