Re: [PATCH 7/8] KVM: Optimize kvm_read_cr[04]_bits()

[Jan Kiszka <jan.kiszka@web.de>]

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Avi Kivity wrote:
> 'mask' is always a constant, so we can check whether it includes a bit that
> might be owned by the guest very cheaply, and avoid the decache call.  Saves
> a few hundred bytes of module text.

-no-kvm-irqchip -smp 2 is broken for my Linux guests since this commit.
Their user space applications receive #UD and things fall apart.

Jan

> 
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
>  arch/x86/kvm/kvm_cache_regs.h |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
> index 6b419a3..5a109c6 100644
> --- a/arch/x86/kvm/kvm_cache_regs.h
> +++ b/arch/x86/kvm/kvm_cache_regs.h
> @@ -1,6 +1,9 @@
>  #ifndef ASM_KVM_CACHE_REGS_H
>  #define ASM_KVM_CACHE_REGS_H
>  
> +#define KVM_POSSIBLE_CR0_GUEST_BITS X86_CR0_TS
> +#define KVM_POSSIBLE_CR4_GUEST_BITS X86_CR4_PGE
> +
>  static inline unsigned long kvm_register_read(struct kvm_vcpu *vcpu,
>  					      enum kvm_reg reg)
>  {
> @@ -40,7 +43,8 @@ static inline u64 kvm_pdptr_read(struct kvm_vcpu *vcpu, int index)
>  
>  static inline ulong kvm_read_cr0_bits(struct kvm_vcpu *vcpu, ulong mask)
>  {
> -	if (mask & vcpu->arch.cr0_guest_owned_bits)
> +	ulong tmask = mask & KVM_POSSIBLE_CR0_GUEST_BITS;
> +	if (tmask & vcpu->arch.cr0_guest_owned_bits)
>  		kvm_x86_ops->decache_cr0_guest_bits(vcpu);
>  	return vcpu->arch.cr0 & mask;
>  }
> @@ -52,7 +56,8 @@ static inline ulong kvm_read_cr0(struct kvm_vcpu *vcpu)
>  
>  static inline ulong kvm_read_cr4_bits(struct kvm_vcpu *vcpu, ulong mask)
>  {
> -	if (mask & vcpu->arch.cr4_guest_owned_bits)
> +	ulong tmask = mask & KVM_POSSIBLE_CR4_GUEST_BITS;
> +	if (tmask & vcpu->arch.cr4_guest_owned_bits)
>  		kvm_x86_ops->decache_cr4_guest_bits(vcpu);
>  	return vcpu->arch.cr4 & mask;
>  }



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