linux-kernel - Re: [PATCH 61/61] KVM: x86: Move VMX's host

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Date:   Tue, 25 Feb 2020 16:02:53 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 61/61] KVM: x86: Move VMX's host_efer to common x86 code

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Move host_efer to common x86 code and use it for CPUID's is_efer_nx() to
> avoid constantly re-reading the MSR.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 ++
>  arch/x86/kvm/cpuid.c            | 5 +----
>  arch/x86/kvm/vmx/vmx.c          | 3 ---
>  arch/x86/kvm/vmx/vmx.h          | 1 -
>  arch/x86/kvm/x86.c              | 5 +++++
>  5 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4165d3ef11e4..a2a091d328c6 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1257,6 +1257,8 @@ struct kvm_arch_async_pf {
>  	bool direct_map;
>  };
>  
> +extern u64 __read_mostly host_efer;
> +

I'm surprised we don't actually cache MSR_EFER in some common x86 code
already.

>  extern struct kvm_x86_ops *kvm_x86_ops;
>  extern struct kmem_cache *x86_fpu_cache;
>  
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 3d287fc6eb6e..e8beb1e542a8 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -134,10 +134,7 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>  
>  static int is_efer_nx(void)
>  {
> -	unsigned long long efer = 0;
> -
> -	rdmsrl_safe(MSR_EFER, &efer);
> -	return efer & EFER_NX;
> +	return host_efer & EFER_NX;
>  }
>  
>  static void cpuid_fix_nx_cap(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e349689ac0cf..0009066e2009 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -433,7 +433,6 @@ static const struct kvm_vmx_segment_field {
>  	VMX_SEGMENT_FIELD(LDTR),
>  };
>  
> -u64 host_efer;
>  static unsigned long host_idt_base;
>  
>  /*
> @@ -7577,8 +7576,6 @@ static __init int hardware_setup(void)
>  	struct desc_ptr dt;
>  	int r, i, ept_lpage_level;
>  
> -	rdmsrl_safe(MSR_EFER, &host_efer);
> -
>  	store_idt(&dt);
>  	host_idt_base = dt.address;
>  
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 70eafa88876a..0e50fbcb8413 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -12,7 +12,6 @@
>  #include "vmcs.h"
>  
>  extern const u32 vmx_msr_index[];
> -extern u64 host_efer;
>  
>  extern u32 get_umwait_control_msr(void);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b40488fd2969..2103101eca78 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -185,6 +185,9 @@ static struct kvm_shared_msrs __percpu *shared_msrs;
>  				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>  				| XFEATURE_MASK_PKRU)
>  
> +u64 __read_mostly host_efer;
> +EXPORT_SYMBOL_GPL(host_efer);
> +
>  static u64 __read_mostly host_xss;
>  
>  struct kvm_stats_debugfs_item debugfs_entries[] = {
> @@ -9590,6 +9593,8 @@ int kvm_arch_hardware_setup(void)
>  {
>  	int r;
>  
> +	rdmsrl_safe(MSR_EFER, &host_efer);
> +
>  	kvm_set_cpu_caps();
>  
>  	r = kvm_x86_ops->hardware_setup();

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly