Snapshot the host's MSR_IA32_ARCH_CAPABILITIES, if it's supported, instead
of reading the MSR every time KVM wants to query the host state, e.g. when
initializing the default value during vCPU creation. The paths that query
ARCH_CAPABILITIES aren't particularly performance sensitive, but creating
vCPUs is a frequent enough operation that burning 8 bytes is a good
trade-off.
Alternatively, KVM could add a field in kvm_caps and thus skip the
on-demand calculations entirely, but a pure snapshot isn't possible due to
the way KVM handles the l1tf_vmx_mitigation module param. And unlike the
other "supported" fields in kvm_caps, KVM doesn't enforce the "supported"
value, i.e. KVM treats ARCH_CAPABILITIES like a CPUID leaf and lets
userspace advertise whatever it wants. Those problems are solvable, but
it's not clear there is real benefit versus snapshotting the host value,
and grabbing the host value will allow additional cleanup of KVM's
FB_CLEAR_CTRL code.
Link: https://lore.kernel.org/all/20230524061634.54141-2-chao.gao@intel.com
Cc: Chao Gao <chao.gao@intel.com>
Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20230607004311.1420507-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
return 0;
}
- if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) {
- u64 msr;
-
- rdmsrl(MSR_IA32_ARCH_CAPABILITIES, msr);
- if (msr & ARCH_CAP_SKIP_VMENTRY_L1DFLUSH) {
- l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
- return 0;
- }
+ if (host_arch_capabilities & ARCH_CAP_SKIP_VMENTRY_L1DFLUSH) {
+ l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
+ return 0;
}
/* If set to auto use the default l1tf mitigation method */
static void vmx_setup_fb_clear_ctrl(void)
{
- u64 msr;
-
- if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES) &&
+ if ((host_arch_capabilities & ARCH_CAP_FB_CLEAR_CTRL) &&
!boot_cpu_has_bug(X86_BUG_MDS) &&
- !boot_cpu_has_bug(X86_BUG_TAA)) {
- rdmsrl(MSR_IA32_ARCH_CAPABILITIES, msr);
- if (msr & ARCH_CAP_FB_CLEAR_CTRL)
- vmx_fb_clear_ctrl_available = true;
- }
+ !boot_cpu_has_bug(X86_BUG_TAA))
+ vmx_fb_clear_ctrl_available = true;
}
static __always_inline void vmx_disable_fb_clear(struct vcpu_vmx *vmx)
u64 __read_mostly host_xss;
EXPORT_SYMBOL_GPL(host_xss);
+u64 __read_mostly host_arch_capabilities;
+EXPORT_SYMBOL_GPL(host_arch_capabilities);
+
const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
KVM_GENERIC_VM_STATS(),
STATS_DESC_COUNTER(VM, mmu_shadow_zapped),
static u64 kvm_get_arch_capabilities(void)
{
- u64 data = 0;
-
- if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) {
- rdmsrl(MSR_IA32_ARCH_CAPABILITIES, data);
- data &= KVM_SUPPORTED_ARCH_CAP;
- }
+ u64 data = host_arch_capabilities & KVM_SUPPORTED_ARCH_CAP;
/*
* If nx_huge_pages is enabled, KVM's shadow paging will ensure that
kvm_init_pmu_capability(ops->pmu_ops);
+ if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
+ rdmsrl(MSR_IA32_ARCH_CAPABILITIES, host_arch_capabilities);
+
r = ops->hardware_setup();
if (r != 0)
goto out_mmu_exit;
extern u64 host_xcr0;
extern u64 host_xss;
+extern u64 host_arch_capabilities;
extern struct kvm_caps kvm_caps;