[PATCH v10 7/9] KVM: VMX: virtualize split lock detection

[Xiaoyao Li]

TEST_CTRL MSR is per-core scope, i.e., the sibling threads in the same
physical core share the same MSR. This requires additional constraint
when exposing it to guest.

1) When host SLD state is sld_off (no X86_FEATURE_SPLIT_LOCK_DETECT),
   feature split lock detection is unsupported/disabled.
   Cannot expose it to guest.

2) When host SLD state is sld_warn (has X86_FEATURE_SPLIT_LOCK_DETECT
   but no X86_FEATURE_SLD_FATAL), feature split lock detection can be
   exposed to guest only when nosmt due to the per-core scope.

   In this case, guest's setting can be propagated into real hardware
   MSR. Further, to avoid the potiential MSR_TEST_CTRL.SLD toggling
   overhead during every vm-enter and vm-exit, it loads and keeps
   guest's SLD setting when in vcpu run loop and guest_state_loaded,
   i.e., between vmx_prepare_switch_to_guest() and
   vmx_prepare_switch_to_host().

3) when host SLD state is sld_fatal (has X86_FEATURE_SLD_FATAL),
   feature split lock detection can be exposed to guest regardless of
   SMT but KVM_HINTS_SLD_FATAL needs to be set.

   In this case, guest can still set and clear MSR_TEST_CTRL.SLD bit,
   but the bit value never be propagated to real MSR. KVM always keeps
   SLD bit turned on for guest vcpu. The reason why not force guest
   MSR_CTRL.SLD bit to 1 is that guest needs to set this bit to 1 itself
   to tell KVM it's SLD-aware.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c   |  6 ++++
 arch/x86/kvm/vmx/vmx.c | 68 ++++++++++++++++++++++++++++++++++++------
 arch/x86/kvm/vmx/vmx.h |  3 ++
 arch/x86/kvm/x86.c     |  6 +++-
 arch/x86/kvm/x86.h     | 16 ++++++++++
 5 files changed, 89 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 3fd6eec202d7..58d902fb12c0 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -751,9 +751,15 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		if (sched_info_on())
 			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
 
+		if (kvm_split_lock_detect_supported())
+			entry->eax |= (1 << KVM_FEATURE_SPLIT_LOCK_DETECT);
+
 		entry->ebx = 0;
 		entry->ecx = 0;
 		entry->edx = 0;
+
+		if (boot_cpu_has(X86_FEATURE_SLD_FATAL))
+			entry->edx |= (1 << KVM_HINTS_SLD_FATAL);
 		break;
 	case 0x80000000:
 		entry->eax = min(entry->eax, 0x8000001f);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e113c9171bcc..e806c2855c9e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1123,6 +1123,29 @@ void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
 	}
 }
 
+static inline u64 vmx_msr_test_ctrl_valid_bits(struct vcpu_vmx *vmx)
+{
+	u64 valid_bits = 0;
+
+	if (vmx->guest_has_sld)
+		valid_bits |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
+
+	return valid_bits;
+}
+
+static inline bool guest_sld_on(struct vcpu_vmx *vmx)
+{
+	return vmx->msr_test_ctrl & MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
+}
+
+static inline void vmx_update_guest_sld(struct vcpu_vmx *vmx)
+{
+	preempt_disable();
+	if (vmx->guest_state_loaded)
+		split_lock_set_guest(guest_sld_on(vmx));
+	preempt_enable();
+}
+
 void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -1191,6 +1214,10 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 #endif
 
 	vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base);
+
+	if (static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) && vmx->guest_has_sld)
+		vmx->host_sld_on = split_lock_set_guest(guest_sld_on(vmx));
+
 	vmx->guest_state_loaded = true;
 }
 
@@ -1229,6 +1256,10 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
 	wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
 #endif
 	load_fixmap_gdt(raw_smp_processor_id());
+
+	if (static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) && vmx->guest_has_sld)
+		split_lock_restore_host(vmx->host_sld_on);
+
 	vmx->guest_state_loaded = false;
 	vmx->guest_msrs_ready = false;
 }
@@ -1833,7 +1864,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 	switch (msr_info->index) {
 	case MSR_TEST_CTRL:
-		msr_info->data = 0;
+		msr_info->data = vmx->msr_test_ctrl;
 		break;
 #ifdef CONFIG_X86_64
 	case MSR_FS_BASE:
@@ -1999,9 +2030,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 	switch (msr_index) {
 	case MSR_TEST_CTRL:
-		if (data)
+		if (data & ~vmx_msr_test_ctrl_valid_bits(vmx))
 			return 1;
 
+		vmx->msr_test_ctrl = data;
+		vmx_update_guest_sld(vmx);
+
 		break;
 	case MSR_EFER:
 		ret = kvm_set_msr_common(vcpu, msr_info);
@@ -4380,7 +4414,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
-
+	vmx->msr_test_ctrl = 0;
 	vmx->msr_ia32_umwait_control = 0;
 
 	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
@@ -4731,24 +4765,32 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static inline bool guest_alignment_check_enabled(struct kvm_vcpu *vcpu)
+{
+	return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
+	       (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+}
+
 /*
  * If the host has split lock detection disabled, then #AC is
  * unconditionally injected into the guest, which is the pre split lock
  * detection behaviour.
  *
  * If the host has split lock detection enabled then #AC is
- * only injected into the guest when:
- *  - Guest CPL == 3 (user mode)
- *  - Guest has #AC detection enabled in CR0
- *  - Guest EFLAGS has AC bit set
+ * injected into the guest when:
+ * 1) guest has alignment check enabled;
+ * or 2) guest has split lock detection enabled;
  */
 static inline bool guest_inject_ac(struct kvm_vcpu *vcpu)
 {
 	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
 		return true;
 
-	return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
-	       (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+	/*
+	 * A split lock access must be an unaligned access, so we should check
+	 * guest_cpu_alignent_check_enabled() fisrt.
+	 */
+	return guest_alignment_check_enabled(vcpu) || guest_sld_on(to_vmx(vcpu));
 }
 
 static int handle_exception_nmi(struct kvm_vcpu *vcpu)
@@ -7316,6 +7358,7 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct kvm_cpuid_entry2 *best;
 
 	/* xsaves_enabled is recomputed in vmx_compute_secondary_exec_control(). */
 	vcpu->arch.xsaves_enabled = false;
@@ -7351,6 +7394,13 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			vmx_set_guest_msr(vmx, msr, enabled ? 0 : TSX_CTRL_RTM_DISABLE);
 		}
 	}
+
+	vmx->guest_has_sld = false;
+	if (kvm_split_lock_detect_supported()) {
+		best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
+		if (best && (best->eax & 1 << KVM_FEATURE_SPLIT_LOCK_DETECT))
+			vmx->guest_has_sld = true;
+	}
 }
 
 static __init void vmx_set_cpu_caps(void)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 26175a4759fa..0714b183ebd2 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -222,12 +222,15 @@ struct vcpu_vmx {
 	int                   nmsrs;
 	int                   save_nmsrs;
 	bool                  guest_msrs_ready;
+	bool                  guest_has_sld;
+	bool                  host_sld_on;
 #ifdef CONFIG_X86_64
 	u64		      msr_host_kernel_gs_base;
 	u64		      msr_guest_kernel_gs_base;
 #endif
 
 	u64		      spec_ctrl;
+	u64                   msr_test_ctrl;
 	u32		      msr_ia32_umwait_control;
 
 	u32 secondary_exec_control;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 599d73206299..36a16a5d924f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1203,7 +1203,7 @@ static const u32 msrs_to_save_all[] = {
 #endif
 	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
 	MSR_IA32_FEAT_CTL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
-	MSR_IA32_SPEC_CTRL,
+	MSR_IA32_SPEC_CTRL, MSR_TEST_CTRL,
 	MSR_IA32_RTIT_CTL, MSR_IA32_RTIT_STATUS, MSR_IA32_RTIT_CR3_MATCH,
 	MSR_IA32_RTIT_OUTPUT_BASE, MSR_IA32_RTIT_OUTPUT_MASK,
 	MSR_IA32_RTIT_ADDR0_A, MSR_IA32_RTIT_ADDR0_B,
@@ -5377,6 +5377,10 @@ static void kvm_init_msr_list(void)
 		 * to the guests in some cases.
 		 */
 		switch (msrs_to_save_all[i]) {
+		case MSR_TEST_CTRL:
+			if (!kvm_split_lock_detect_supported())
+				continue;
+			break;
 		case MSR_IA32_BNDCFGS:
 			if (!kvm_mpx_supported())
 				continue;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 995ab696dcf0..c65871fe3661 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -367,6 +367,22 @@ static inline bool kvm_dr6_valid(u64 data)
 	return !(data >> 32);
 }
 
+/*
+ * Since MSR_TEST is per-core scope, feature split lock detection cannot be
+ * exposed to guest when smt is possible() and !X86_FEATURE_SLD_FATAL. In this
+ * case, kvm needs to prograte the guest's value to real hardware MSR which
+ * can change the value of sibling threads.
+ *
+ * When X86_FEATURE_SLD_FATAL, we don't need to worry about the smt issue.
+ * Because in this case, the hardware MSR_TEST_CTRL.SLD bit is always set.
+ */
+static inline bool kvm_split_lock_detect_supported(void)
+{
+	return boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
+	       (boot_cpu_has(X86_FEATURE_SLD_FATAL) ||
+		!cpu_smt_possible());
+}
+
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
 int kvm_spec_ctrl_test_value(u64 value);
-- 
2.18.4