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Date: Thu, 13 Feb 2020 22:21:26 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...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 20/61] KVM: x86: Calculate the supported xcr0 mask at load
time
On 2/2/2020 2:51 AM, Sean Christopherson wrote:
> Add a new global variable, supported_xcr0, to track which xcr0 bits can
> be exposed to the guest instead of calculating the mask on every call.
> The supported bits are constant for a given instance of KVM.
>
> This paves the way toward eliminating the ->mpx_supported() call in
> kvm_mpx_supported(), e.g. eliminates multiple retpolines in VMX's nested
> VM-Enter path, and eventually toward eliminating ->mpx_supported()
> altogether.
>
> No functional change intended.
>
Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
> arch/x86/kvm/cpuid.c | 32 +++++++++-----------------------
> arch/x86/kvm/svm.c | 2 ++
> arch/x86/kvm/vmx/vmx.c | 4 ++++
> arch/x86/kvm/x86.c | 14 +++++++++++---
> arch/x86/kvm/x86.h | 7 +------
> 5 files changed, 27 insertions(+), 32 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index bfd8304a8437..b9763eb711cb 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -52,16 +52,6 @@ bool kvm_mpx_supported(void)
> }
> EXPORT_SYMBOL_GPL(kvm_mpx_supported);
>
> -u64 kvm_supported_xcr0(void)
> -{
> - u64 xcr0 = KVM_SUPPORTED_XCR0 & host_xcr0;
> -
> - if (!kvm_mpx_supported())
> - xcr0 &= ~(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
> -
> - return xcr0;
> -}
> -
> #define F feature_bit
>
> int kvm_update_cpuid(struct kvm_vcpu *vcpu)
> @@ -107,8 +97,7 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
> vcpu->arch.guest_xstate_size = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
> } else {
> vcpu->arch.guest_supported_xcr0 =
> - (best->eax | ((u64)best->edx << 32)) &
> - kvm_supported_xcr0();
> + (best->eax | ((u64)best->edx << 32)) & supported_xcr0;
> vcpu->arch.guest_xstate_size = best->ebx =
> xstate_required_size(vcpu->arch.xcr0, false);
> }
> @@ -633,14 +622,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> goto out;
> }
> break;
> - case 0xd: {
> - u64 supported = kvm_supported_xcr0();
> -
> - entry->eax &= supported;
> - entry->ebx = xstate_required_size(supported, false);
> + case 0xd:
> + entry->eax &= supported_xcr0;
> + entry->ebx = xstate_required_size(supported_xcr0, false);
> entry->ecx = entry->ebx;
> - entry->edx &= supported >> 32;
> - if (!supported)
> + entry->edx &= supported_xcr0 >> 32;
> + if (!supported_xcr0)
> break;
>
> entry = do_host_cpuid(array, function, 1);
> @@ -650,7 +637,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> entry->eax &= kvm_cpuid_D_1_eax_x86_features;
> cpuid_mask(&entry->eax, CPUID_D_1_EAX);
> if (entry->eax & (F(XSAVES)|F(XSAVEC)))
> - entry->ebx = xstate_required_size(supported, true);
> + entry->ebx = xstate_required_size(supported_xcr0, true);
> else
> entry->ebx = 0;
> /* Saving XSS controlled state via XSAVES isn't supported. */
> @@ -658,7 +645,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> entry->edx = 0;
>
> for (i = 2; i < 64; ++i) {
> - if (!(supported & BIT_ULL(i)))
> + if (!(supported_xcr0 & BIT_ULL(i)))
> continue;
>
> entry = do_host_cpuid(array, function, i);
> @@ -666,7 +653,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> goto out;
>
> /*
> - * The @supported check above should have filtered out
> + * The supported check above should have filtered out
> * invalid sub-leafs as well as sub-leafs managed by
> * IA32_XSS MSR. Only XCR0-managed sub-leafs should
> * reach this point, and they should have a non-zero
> @@ -681,7 +668,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> entry->edx = 0;
> }
> break;
> - }
> /* Intel PT */
> case 0x14:
> if (!f_intel_pt)
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index bf0556588ad0..af096c4f9c5f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1368,6 +1368,8 @@ static __init int svm_hardware_setup(void)
>
> init_msrpm_offsets();
>
> + supported_xcr0 &= ~(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
> +
> if (boot_cpu_has(X86_FEATURE_NX))
> kvm_enable_efer_bits(EFER_NX);
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 588aa5e4164e..32a84ec15064 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7590,6 +7590,10 @@ static __init int hardware_setup(void)
> WARN_ONCE(host_bndcfgs, "KVM: BNDCFGS in host will be lost");
> }
>
> + if (!kvm_mpx_supported())
> + supported_xcr0 &= ~(XFEATURE_MASK_BNDREGS |
> + XFEATURE_MASK_BNDCSR);
> +
> if (!cpu_has_vmx_vpid() || !cpu_has_vmx_invvpid() ||
> !(cpu_has_vmx_invvpid_single() || cpu_has_vmx_invvpid_global()))
> enable_vpid = 0;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7e3f1d937224..f90c56c0c64a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -180,6 +180,11 @@ struct kvm_shared_msrs {
> static struct kvm_shared_msrs_global __read_mostly shared_msrs_global;
> static struct kvm_shared_msrs __percpu *shared_msrs;
>
> +#define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
> + | XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
> + | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
> + | XFEATURE_MASK_PKRU)
> +
> static u64 __read_mostly host_xss;
>
> struct kvm_stats_debugfs_item debugfs_entries[] = {
> @@ -226,6 +231,8 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> };
>
> u64 __read_mostly host_xcr0;
> +u64 __read_mostly supported_xcr0;
> +EXPORT_SYMBOL_GPL(supported_xcr0);
>
> struct kmem_cache *x86_fpu_cache;
> EXPORT_SYMBOL_GPL(x86_fpu_cache);
> @@ -4081,8 +4088,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
> * CPUID leaf 0xD, index 0, EDX:EAX. This is for compatibility
> * with old userspace.
> */
> - if (xstate_bv & ~kvm_supported_xcr0() ||
> - mxcsr & ~mxcsr_feature_mask)
> + if (xstate_bv & ~supported_xcr0 || mxcsr & ~mxcsr_feature_mask)
> return -EINVAL;
> load_xsave(vcpu, (u8 *)guest_xsave->region);
> } else {
> @@ -7335,8 +7341,10 @@ int kvm_arch_init(void *opaque)
>
> perf_register_guest_info_callbacks(&kvm_guest_cbs);
>
> - if (boot_cpu_has(X86_FEATURE_XSAVE))
> + if (boot_cpu_has(X86_FEATURE_XSAVE)) {
> host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
> + supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
> + }
>
> kvm_lapic_init();
> if (pi_inject_timer == -1)
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 3624665acee4..02b49ee49e24 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -280,13 +280,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> int emulation_type, void *insn, int insn_len);
> enum exit_fastpath_completion handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
>
> -#define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
> - | XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
> - | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
> - | XFEATURE_MASK_PKRU)
> extern u64 host_xcr0;
> -
> -extern u64 kvm_supported_xcr0(void);
> +extern u64 supported_xcr0;
>
> extern unsigned int min_timer_period_us;
>
>
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