KVM: X86: Expose bus lock debug exception to guest

Bus lock debug exception is an ability to notify the kernel by an #DB
trap after the instruction acquires a bus lock and is executed when
CPL>0. This allows the kernel to enforce user application throttling or
mitigations.

Existence of bus lock debug exception is enumerated via
CPUID.(EAX=7,ECX=0).ECX[24]. Software can enable these exceptions by
setting bit 2 of the MSR_IA32_DEBUGCTL. Expose the CPUID to guest and
emulate the MSR handling when guest enables it.

Support for this feature was originally developed by Xiaoyao Li and
Chenyi Qiang, but code has since changed enough that this patch has
nothing in common with theirs, except for this commit message.

Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20210202090433.13441-4-chenyi.qiang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f42e949..9a48f13 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -458,7 +458,7 @@ void kvm_set_cpu_caps(void)
                F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
                F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
                F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/ |
-               F(SGX_LC)
+               F(SGX_LC) | F(BUS_LOCK_DETECT)
        );
        /* Set LA57 based on hardware capability. */
        if (cpuid_ecx(7) & F(LA57))

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index d1d7798..8dee8a5 100644 (file)
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -398,6 +398,9 @@ static inline u64 vmx_supported_debugctl(void)
 {
        u64 debugctl = 0;
 
+       if (boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT))
+               debugctl |= DEBUGCTLMSR_BUS_LOCK_DETECT;
+
        if (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT)
                debugctl |= DEBUGCTLMSR_LBR_MASK;
 

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 61f7e52..f2fd447 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2014,6 +2014,9 @@ static u64 vcpu_supported_debugctl(struct kvm_vcpu *vcpu)
        if (!intel_pmu_lbr_is_enabled(vcpu))
                debugctl &= ~DEBUGCTLMSR_LBR_MASK;
 
+       if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+               debugctl &= ~DEBUGCTLMSR_BUS_LOCK_DETECT;
+
        return debugctl;
 }