[PATCH 09/26] KVM: x86: Calculate the supported xcr0 mask at load time

Sean Christopherson
2020-01-29T23:48:11Z

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.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/cpuid.c | 15 ++-------------
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, 20 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b1c469446b07..51b604c9a3f5 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);
}
@@ -644,7 +633,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
}
case 0xd: {
int idx, i;
- u64 supported = kvm_supported_xcr0();
+ u64 supported = supported_xcr0;

entry->eax &= supported;
entry->ebx = xstate_required_size(supported, false);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index df4d0b6f31c8..f3e6dcefc094 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 ed63219ca52e..f16c1faf6ced 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7620,6 +7620,10 @@ 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 adbdbe785f05..03e656d05c15 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 {
@@ -7310,8 +7316,10 @@ 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;

--
2.24.1