[PATCH v2 39/66] KVM: SVM: Convert feature updates from CPUID to KVM cpu caps

Sean Christopherson
2020-03-02T23:57:26Z

Use the recently introduced KVM CPU caps to propagate SVM-only (kernel)
settings to supported CPUID flags.

Note, there are a few subtleties:

- Setting a flag based on a *different* feature is effectively
emulation, and must be done at runtime via ->set_supported_cpuid().

- CPUID 0x8000000A.EDX is a feature leaf that was previously not
adjusted by kvm_cpu_cap_mask() because all features are hidden by
default.

Opportunistically add a technically unnecessary break and fix an
indentation issue in svm_set_supported_cpuid().

No functional change intended.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/cpuid.c | 6 ++++++
arch/x86/kvm/svm.c | 51 +++++++++++++++++++++++++++-----------------
2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f0b6885d2415..e26644d8280b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -376,6 +376,12 @@ void kvm_set_cpu_caps(void)
F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON)
);

+ /*
+ * Hide all SVM features by default, SVM will set the cap bits for
+ * features it emulates and/or exposes for L1.
+ */
+ kvm_cpu_cap_mask(CPUID_8000_000A_EDX, 0);
+
kvm_cpu_cap_mask(CPUID_C000_0001_EDX,
F(XSTORE) | F(XSTORE_EN) | F(XCRYPT) | F(XCRYPT_EN) |
F(ACE2) | F(ACE2_EN) | F(PHE) | F(PHE_EN) |
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 0725a67e3480..8ce07f6ebe8e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1367,6 +1367,25 @@ static void svm_hardware_teardown(void)
iopm_base = 0;
}

+static __init void svm_set_cpu_caps(void)
+{
+ /* CPUID 0x1 */
+ if (avic)
+ kvm_cpu_cap_clear(X86_FEATURE_X2APIC);
+
+ /* CPUID 0x80000001 */
+ if (nested)
+ kvm_cpu_cap_set(X86_FEATURE_SVM);
+
+ /* CPUID 0x8000000A */
+ /* Support next_rip if host supports it */
+ if (boot_cpu_has(X86_FEATURE_NRIPS))
+ kvm_cpu_cap_set(X86_FEATURE_NRIPS);
+
+ if (npt_enabled)
+ kvm_cpu_cap_set(X86_FEATURE_NPT);
+}
+
static __init int svm_hardware_setup(void)
{
int cpu;
@@ -1479,6 +1498,8 @@ static __init int svm_hardware_setup(void)
pr_info("Virtual GIF supported\n");
}

+ svm_set_cpu_caps();
+
return 0;

err:
@@ -6027,20 +6048,20 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu)
APICV_INHIBIT_REASON_NESTED);
}

+/*
+ * Vendor specific emulation must be handled via ->set_supported_cpuid(), not
+ * svm_set_cpu_caps(), as capabilities configured during hardware_setup() are
+ * masked against hardware/kernel support, i.e. they'd be lost.
+ *
+ * Note, setting a flag based on a *different* feature, e.g. setting VIRT_SSBD
+ * if LS_CFG_SSBD or AMD_SSBD is supported, is effectively emulation.
+ */
static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
{
switch (entry->function) {
- case 0x1:
- if (avic)
- cpuid_entry_clear(entry, X86_FEATURE_X2APIC);
- break;
- case 0x80000001:
- if (nested)
- cpuid_entry_set(entry, X86_FEATURE_SVM);
- break;
case 0x80000008:
if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
- boot_cpu_has(X86_FEATURE_AMD_SSBD))
+ boot_cpu_has(X86_FEATURE_AMD_SSBD))
cpuid_entry_set(entry, X86_FEATURE_VIRT_SSBD);
break;
case 0x8000000A:
@@ -6048,16 +6069,8 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
ASID emulation to nested SVM */
entry->ecx = 0; /* Reserved */
- entry->edx = 0; /* Per default do not support any
- additional features */
-
- /* Support next_rip if host supports it */
- if (boot_cpu_has(X86_FEATURE_NRIPS))
- cpuid_entry_set(entry, X86_FEATURE_NRIPS);
-
- /* Support NPT for the guest if enabled */
- if (npt_enabled)
- cpuid_entry_set(entry, X86_FEATURE_NPT);
+ /* Note, 0x8000000A.EDX is managed via kvm_cpu_caps. */;
+ break;
}
}

--
2.24.1