Re: [PATCH v4 2/2] x86/kvm/fpu: Remove kvm_vcpu_arch.guest_supported_xcr0

[David Edmondson <david.edmondson@oracle.com>]

On Thursday, 2022-02-17 at 02:30:30 -03, Leonardo Bras wrote:

> kvm_vcpu_arch currently contains the guest supported features in both
> guest_supported_xcr0 and guest_fpu.fpstate->user_xfeatures field.
>
> Currently both fields are set to the same value in
> kvm_vcpu_after_set_cpuid() and are not changed anywhere else after that.
>
> Since it's not good to keep duplicated data, remove guest_supported_xcr0.
>
> To keep the code more readable, introduce kvm_guest_supported_xcr()
> and kvm_guest_supported_xfd() to replace the previous usages of
> guest_supported_xcr0.
>
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 -
>  arch/x86/kvm/cpuid.c            |  5 +++--
>  arch/x86/kvm/x86.c              | 20 +++++++++++++++-----
>  3 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6dcccb304775..ec9830d2aabf 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -703,7 +703,6 @@ struct kvm_vcpu_arch {
>  	struct fpu_guest guest_fpu;
>
>  	u64 xcr0;
> -	u64 guest_supported_xcr0;
>
>  	struct kvm_pio_request pio;
>  	void *pio_data;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 71125291c578..b8f8d268d058 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -282,6 +282,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_lapic *apic = vcpu->arch.apic;
>  	struct kvm_cpuid_entry2 *best;
> +	u64 guest_supported_xcr0;

The intermediate variable seems unnecessary.

>
>  	best = kvm_find_cpuid_entry(vcpu, 1, 0);
>  	if (best && apic) {
> @@ -293,10 +294,10 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  		kvm_apic_set_version(vcpu);
>  	}
>
> -	vcpu->arch.guest_supported_xcr0 =
> +	guest_supported_xcr0 =
>  		cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent);
>
> -	vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0;
> +	vcpu->arch.guest_fpu.fpstate->user_xfeatures = guest_supported_xcr0;
>
>  	kvm_update_pv_runtime(vcpu);
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 641044db415d..92177e2ff664 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -984,6 +984,18 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
>  }
>  EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);
>
> +static inline u64 kvm_guest_supported_xcr(struct kvm_vcpu *vcpu)
> +{
> +	u64 guest_supported_xcr0 = vcpu->arch.guest_fpu.fpstate->user_xfeatures;

...and here.

> +
> +	return guest_supported_xcr0;
> +}
> +
> +static inline u64 kvm_guest_supported_xfd(struct kvm_vcpu *vcpu)
> +{
> +	return kvm_guest_supported_xcr(vcpu) & XFEATURE_MASK_USER_DYNAMIC;
> +}
> +
>  static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>  {
>  	u64 xcr0 = xcr;
> @@ -1003,7 +1015,7 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>  	 * saving.  However, xcr0 bit 0 is always set, even if the
>  	 * emulated CPU does not support XSAVE (see kvm_vcpu_reset()).
>  	 */
> -	valid_bits = vcpu->arch.guest_supported_xcr0 | XFEATURE_MASK_FP;
> +	valid_bits = kvm_guest_supported_xcr(vcpu) | XFEATURE_MASK_FP;
>  	if (xcr0 & ~valid_bits)
>  		return 1;
>
> @@ -3706,8 +3718,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
>  			return 1;
>
> -		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
> -			     vcpu->arch.guest_supported_xcr0))
> +		if (data & ~(kvm_guest_supported_xfd(vcpu)))

Brackets could be removed...

>  			return 1;
>
>  		fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
> @@ -3717,8 +3728,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
>  			return 1;
>
> -		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
> -			     vcpu->arch.guest_supported_xcr0))
> +		if (data & ~(kvm_guest_supported_xfd(vcpu)))

...and here.

>  			return 1;
>
>  		vcpu->arch.guest_fpu.xfd_err = data;

dme.
-- 
But he said, leave me alone, I'm a family man.