Re: [PATCH 6/9] KVM: x86: Update guest cpu_caps at runtime for dynamic CPUID-based features

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 11/11/2023 7:55 AM, Sean Christopherson wrote:
When updating guest CPUID entries to emulate runtime behavior, e.g. when
the guest enables a CR4-based feature that is tied to a CPUID flag, also
update the vCPU's cpu_caps accordingly.  This will allow replacing all
usage of guest_cpuid_has() with guest_cpu_cap_has().

Take care not to update guest capabilities when KVM is updating CPUID
entries that *may* become the vCPU's CPUID, e.g. if userspace tries to set
bogus CPUID information.  No extra call to update cpu_caps is needed as
the cpu_caps are initialized from the incoming guest CPUID, i.e. will
automatically get the updated values.

Note, none of the features in question use guest_cpu_cap_has() at this
time, i.e. aside from settings bits in cpu_caps, this is a glorified nop.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
  arch/x86/kvm/cpuid.c | 48 +++++++++++++++++++++++++++++++-------------
  1 file changed, 34 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 36bd04030989..37a991439fe6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -262,31 +262,48 @@ static u64 cpuid_get_supported_xcr0(struct kvm_cpuid_entry2 *entries, int nent)
  	return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
  }
+static __always_inline void kvm_update_feature_runtime(struct kvm_vcpu *vcpu,
+						       struct kvm_cpuid_entry2 *entry,
+						       unsigned int x86_feature,
+						       bool has_feature)
+{
+	if (entry)
+		cpuid_entry_change(entry, x86_feature, has_feature);
+
+	if (vcpu)
+		guest_cpu_cap_change(vcpu, x86_feature, has_feature);
+}
+
  static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *entries,
  				       int nent)
  {
  	struct kvm_cpuid_entry2 *best;
+	struct kvm_vcpu *caps = vcpu;

u32 *caps  = vcpu->arch.cpu_caps;
and update guest_cpu_cap_set(), guest_cpu_cap_clear(), guest_cpu_cap_change() and guest_cpu_cap_restrict() to pass in vcpu->arch.cpu_caps instead of vcpu, since all of them merely refer to vcpu cap, rather than whole vcpu info.

Or, for simple change, here rename variable name "caps" --> "vcpu", to less reading confusion.

+
+	/*
+	 * Don't update vCPU capabilities if KVM is updating CPUID entries that
+	 * are coming in from userspace!
+	 */
+	if (entries != vcpu->arch.cpuid_entries)
+		caps = NULL;
best = cpuid_entry2_find(entries, nent, 1, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
-	if (best) {
-		/* Update OSXSAVE bit */
-		if (boot_cpu_has(X86_FEATURE_XSAVE))
-			cpuid_entry_change(best, X86_FEATURE_OSXSAVE,
+
+	if (boot_cpu_has(X86_FEATURE_XSAVE))
+		kvm_update_feature_runtime(caps, best, X86_FEATURE_OSXSAVE,
  					   kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE));
- cpuid_entry_change(best, X86_FEATURE_APIC,
-			   vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE);
+	kvm_update_feature_runtime(caps, best, X86_FEATURE_APIC,
+				   vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE);
- if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT))
-			cpuid_entry_change(best, X86_FEATURE_MWAIT,
-					   vcpu->arch.ia32_misc_enable_msr &
-					   MSR_IA32_MISC_ENABLE_MWAIT);
-	}
+	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT))
+		kvm_update_feature_runtime(caps, best, X86_FEATURE_MWAIT,
+					   vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_MWAIT);
best = cpuid_entry2_find(entries, nent, 7, 0);
-	if (best && boot_cpu_has(X86_FEATURE_PKU))
-		cpuid_entry_change(best, X86_FEATURE_OSPKE,
-				   kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE));
+	if (boot_cpu_has(X86_FEATURE_PKU))
+		kvm_update_feature_runtime(caps, best, X86_FEATURE_OSPKE,
+					   kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE));
best = cpuid_entry2_find(entries, nent, 0xD, 0);
  	if (best)
@@ -353,6 +370,9 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
  	 * Reset guest capabilities to userspace's guest CPUID definition, i.e.
  	 * honor userspace's definition for features that don't require KVM or
  	 * hardware management/support (or that KVM simply doesn't care about).
+	 *
+	 * Note, KVM has already done runtime updates on guest CPUID, i.e. this
+	 * will also correctly set runtime features in guest CPU capabilities.
  	 */
  	for (i = 0; i < NR_KVM_CPU_CAPS; i++) {
  		const struct cpuid_reg cpuid = reverse_cpuid[i];





[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux