linux-kernel - Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU

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Message-ID: <8b7cd59e-05b9-e8c4-b686-8a3fda88c191@gmail.com>
Date:   Thu, 24 Aug 2017 17:09:19 +0800
From:   Yang Zhang <yang.zhang.wz@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     junkang.fjk@...baba-inc.com
Subject: Re: [PATCH 1/2] KVM: x86: simplify handling of PKRU

On 2017/8/24 5:26, Paolo Bonzini wrote:
> Move it to struct kvm_arch_vcpu, replacing guest_pkru_valid with a
> simple comparison against the host value of the register.

Thanks for refine the patches.:)

> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/kvm_cache_regs.h   |  5 -----
>   arch/x86/kvm/mmu.h              |  2 +-
>   arch/x86/kvm/svm.c              |  7 -------
>   arch/x86/kvm/vmx.c              | 23 ++++++-----------------
>   5 files changed, 8 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 643308143bea..beb185361045 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -491,6 +491,7 @@ struct kvm_vcpu_arch {
>   	unsigned long cr4;
>   	unsigned long cr4_guest_owned_bits;
>   	unsigned long cr8;
> +	u32 pkru;
>   	u32 hflags;
>   	u64 efer;
>   	u64 apic_base;
> diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
> index 762cdf2595f9..e1e89ee4af75 100644
> --- a/arch/x86/kvm/kvm_cache_regs.h
> +++ b/arch/x86/kvm/kvm_cache_regs.h
> @@ -84,11 +84,6 @@ static inline u64 kvm_read_edx_eax(struct kvm_vcpu *vcpu)
>   		| ((u64)(kvm_register_read(vcpu, VCPU_REGS_RDX) & -1u) << 32);
>   }
>   
> -static inline u32 kvm_read_pkru(struct kvm_vcpu *vcpu)
> -{
> -	return kvm_x86_ops->get_pkru(vcpu);
> -}
> -
>   static inline void enter_guest_mode(struct kvm_vcpu *vcpu)
>   {
>   	vcpu->arch.hflags |= HF_GUEST_MASK;
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 3ed6192d93b1..1b3095264fcf 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -168,7 +168,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>   		* index of the protection domain, so pte_pkey * 2 is
>   		* is the index of the first bit for the domain.
>   		*/
> -		pkru_bits = (kvm_read_pkru(vcpu) >> (pte_pkey * 2)) & 3;
> +		pkru_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
>   
>   		/* clear present bit, replace PFEC.RSVD with ACC_USER_MASK. */
>   		offset = (pfec & ~1) +
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 32c8d8f62985..f2355135164c 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1826,11 +1826,6 @@ static void svm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>   	to_svm(vcpu)->vmcb->save.rflags = rflags;
>   }
>   
> -static u32 svm_get_pkru(struct kvm_vcpu *vcpu)
> -{
> -	return 0;
> -}
> -
>   static void svm_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
>   {
>   	switch (reg) {
> @@ -5438,8 +5433,6 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
>   	.get_rflags = svm_get_rflags,
>   	.set_rflags = svm_set_rflags,
>   
> -	.get_pkru = svm_get_pkru,
> -
>   	.tlb_flush = svm_flush_tlb,
>   
>   	.run = svm_vcpu_run,
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ddabed8425b3..c603f658c42a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -639,8 +639,6 @@ struct vcpu_vmx {
>   
>   	u64 current_tsc_ratio;
>   
> -	bool guest_pkru_valid;
> -	u32 guest_pkru;
>   	u32 host_pkru;
>   
>   	/*
> @@ -2392,11 +2390,6 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>   		to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>   }
>   
> -static u32 vmx_get_pkru(struct kvm_vcpu *vcpu)
> -{
> -	return to_vmx(vcpu)->guest_pkru;
> -}
> -
>   static u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu)
>   {
>   	u32 interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
> @@ -9239,8 +9232,9 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
>   	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
>   		vmx_set_interrupt_shadow(vcpu, 0);
>   
> -	if (vmx->guest_pkru_valid)
> -		__write_pkru(vmx->guest_pkru);
> +	if (static_cpu_has(X86_FEATURE_OSPKE) &&

We expose protection key to VM without check whether OSPKE is enabled or 
not. Why not check guest's cpuid here which also can avoid unnecessary 
access to pkru?

> +	    vcpu->arch.pkru != vmx->host_pkru)
> +		__write_pkru(vcpu->arch.pkru);
>   
>   	atomic_switch_perf_msrs(vmx);
>   	debugctlmsr = get_debugctlmsr();
> @@ -9388,13 +9382,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
>   	 * back on host, so it is safe to read guest PKRU from current
>   	 * XSAVE.
>   	 */
> -	if (boot_cpu_has(X86_FEATURE_OSPKE)) {
> -		vmx->guest_pkru = __read_pkru();
> -		if (vmx->guest_pkru != vmx->host_pkru) {
> -			vmx->guest_pkru_valid = true;
> +	if (static_cpu_has(X86_FEATURE_OSPKE)) {
> +		vcpu->arch.pkru = __read_pkru();
> +		if (vcpu->arch.pkru != vmx->host_pkru)
>   			__write_pkru(vmx->host_pkru);
> -		} else
> -			vmx->guest_pkru_valid = false;
>   	}
>   
>   	/*
> @@ -11875,8 +11866,6 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
>   	.get_rflags = vmx_get_rflags,
>   	.set_rflags = vmx_set_rflags,
>   
> -	.get_pkru = vmx_get_pkru,
> -
>   	.tlb_flush = vmx_flush_tlb,
>   
>   	.run = vmx_vcpu_run,
> 


-- 
Yang
Alibaba Cloud Computing