[RFC v2 2/2] KVM: VMX: Enable bus lock VM exit

From: Chenyi Qiang
Date: Sun Aug 16 2020 - 21:45:13 EST

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Virtual Machine can exploit bus locks to degrade the performance of
system. Bus lock can be caused by split locked access to writeback(WB)
memory or by using locks on uncacheable(UC) memory. The bus lock is
typically >1000 cycles slower than an atomic operation within a cache
line. It also disrupts performance on other cores (which must wait for
the bus lock to be released before their memory operations can
complete).

To address the threat, bus lock VM exit is introduced to notify the VMM
when a bus lock was acquired, allowing it to enforce throttling or other
policy based mitigations.

A VMM can enable VM exit due to bus locks by setting a new "Bus Lock
Detection" VM-execution control(bit 30 of Secondary Processor-based VM
execution controls). If delivery of this VM exit was preempted by a
higher priority VM exit (e.g. EPT misconfiguration, EPT violation, APIC
access VM exit, APIC write VM exit, exception bitmap exiting), bit 26 of
exit reason in vmcs field is set to 1.

In current implementation, the KVM exposes this capability through
KVM_CAP_X86_BLD. The user can set it to enable the bus lock VM exit
(disabled by default). If bus locks in guest are detected by KVM, exit
to user space even when current exit reason is handled by KVM
internally. Set a new field KVM_RUN_BUS_LOCK in vcpu->run->flags to
inform the user space that there is a bus lock in guest and it is
preempted by a higher priority VM exit.

Every bus lock acquired in non-root mode will be recorded in
vcpu->stat.bus_locks and exposed through debugfs when the bus lock
VM exit is enabled.

Document for Bus Lock VM exit is now available at the latest "Intel
Architecture Instruction Set Extensions Programming Reference".

Document Link:
https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html

Co-developed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 9 ++++++++
arch/x86/include/asm/vmx.h | 1 +
arch/x86/include/asm/vmxfeatures.h | 1 +
arch/x86/include/uapi/asm/kvm.h | 1 +
arch/x86/include/uapi/asm/vmx.h | 4 +++-
arch/x86/kvm/vmx/capabilities.h | 6 +++++
arch/x86/kvm/vmx/vmx.c | 33 ++++++++++++++++++++++++++-
arch/x86/kvm/vmx/vmx.h | 2 +-
arch/x86/kvm/x86.c | 36 +++++++++++++++++++++++++++++-
arch/x86/kvm/x86.h | 5 +++++
include/uapi/linux/kvm.h | 2 ++
11 files changed, 96 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index be5363b21540..bfabe2f15b30 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -829,6 +829,9 @@ struct kvm_vcpu_arch {

/* AMD MSRC001_0015 Hardware Configuration */
u64 msr_hwcr;
+
+ /* Set when bus lock VM exit is preempted by a higher priority VM exit */
+ bool bus_lock_detected;
};

struct kvm_lpage_info {
@@ -1002,6 +1005,9 @@ struct kvm_arch {
bool guest_can_read_msr_platform_info;
bool exception_payload_enabled;

+ /* Set when bus lock vm exit is enabled by user */
+ bool bus_lock_exit;
+
struct kvm_pmu_event_filter *pmu_event_filter;
struct task_struct *nx_lpage_recovery_thread;
};
@@ -1051,6 +1057,7 @@ struct kvm_vcpu_stat {
u64 req_event;
u64 halt_poll_success_ns;
u64 halt_poll_fail_ns;
+ u64 bus_locks;
};

struct x86_instruction_info;
@@ -1388,6 +1395,8 @@ extern u8 kvm_tsc_scaling_ratio_frac_bits;
extern u64 kvm_max_tsc_scaling_ratio;
/* 1ull << kvm_tsc_scaling_ratio_frac_bits */
extern u64 kvm_default_tsc_scaling_ratio;
+/* bus lock detection supported */
+extern bool kvm_has_bus_lock_exit;

extern u64 kvm_mce_cap_supported;

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index cd7de4b401fe..93a880bc31a7 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -73,6 +73,7 @@
#define SECONDARY_EXEC_PT_USE_GPA VMCS_CONTROL_BIT(PT_USE_GPA)
#define SECONDARY_EXEC_TSC_SCALING VMCS_CONTROL_BIT(TSC_SCALING)
#define SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE VMCS_CONTROL_BIT(USR_WAIT_PAUSE)
+#define SECONDARY_EXEC_BUS_LOCK_DETECTION VMCS_CONTROL_BIT(BUS_LOCK_DETECTION)

#define PIN_BASED_EXT_INTR_MASK VMCS_CONTROL_BIT(INTR_EXITING)
#define PIN_BASED_NMI_EXITING VMCS_CONTROL_BIT(NMI_EXITING)
diff --git a/arch/x86/include/asm/vmxfeatures.h b/arch/x86/include/asm/vmxfeatures.h
index 9915990fd8cf..e80523346274 100644
--- a/arch/x86/include/asm/vmxfeatures.h
+++ b/arch/x86/include/asm/vmxfeatures.h
@@ -83,5 +83,6 @@
#define VMX_FEATURE_TSC_SCALING ( 2*32+ 25) /* Scale hardware TSC when read in guest */
#define VMX_FEATURE_USR_WAIT_PAUSE ( 2*32+ 26) /* Enable TPAUSE, UMONITOR, UMWAIT in guest */
#define VMX_FEATURE_ENCLV_EXITING ( 2*32+ 28) /* "" VM-Exit on ENCLV (leaf dependent) */
+#define VMX_FEATURE_BUS_LOCK_DETECTION ( 2*32+ 30) /* VM-Exit when bus lock caused */

#endif /* _ASM_X86_VMXFEATURES_H */
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 0780f97c1850..a1471c05f7f9 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -111,6 +111,7 @@ struct kvm_ioapic_state {
#define KVM_NR_IRQCHIPS 3

#define KVM_RUN_X86_SMM (1 << 0)
+#define KVM_RUN_BUS_LOCK (1 << 1)

/* for KVM_GET_REGS and KVM_SET_REGS */
struct kvm_regs {
diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h
index b8ff9e8ac0d5..14c177c4afd5 100644
--- a/arch/x86/include/uapi/asm/vmx.h
+++ b/arch/x86/include/uapi/asm/vmx.h
@@ -88,6 +88,7 @@
#define EXIT_REASON_XRSTORS 64
#define EXIT_REASON_UMWAIT 67
#define EXIT_REASON_TPAUSE 68
+#define EXIT_REASON_BUS_LOCK 74

#define VMX_EXIT_REASONS \
{ EXIT_REASON_EXCEPTION_NMI, "EXCEPTION_NMI" }, \
@@ -148,7 +149,8 @@
{ EXIT_REASON_XSAVES, "XSAVES" }, \
{ EXIT_REASON_XRSTORS, "XRSTORS" }, \
{ EXIT_REASON_UMWAIT, "UMWAIT" }, \
- { EXIT_REASON_TPAUSE, "TPAUSE" }
+ { EXIT_REASON_TPAUSE, "TPAUSE" }, \
+ { EXIT_REASON_BUS_LOCK, "BUS_LOCK" }

#define VMX_EXIT_REASON_FLAGS \
{ VMX_EXIT_REASONS_FAILED_VMENTRY, "FAILED_VMENTRY" }
diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 4bbd8b448d22..aa94535e6705 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -262,6 +262,12 @@ static inline bool cpu_has_vmx_tsc_scaling(void)
SECONDARY_EXEC_TSC_SCALING;
}

+static inline bool cpu_has_vmx_bus_lock_detection(void)
+{
+ return vmcs_config.cpu_based_2nd_exec_ctrl &
+ SECONDARY_EXEC_BUS_LOCK_DETECTION;
+}
+
static inline bool cpu_has_vmx_apicv(void)
{
return cpu_has_vmx_apic_register_virt() &&
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 89c131eaedf2..1560e51d2d8e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2460,7 +2460,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE |
SECONDARY_EXEC_PT_USE_GPA |
SECONDARY_EXEC_PT_CONCEAL_VMX |
- SECONDARY_EXEC_ENABLE_VMFUNC;
+ SECONDARY_EXEC_ENABLE_VMFUNC |
+ SECONDARY_EXEC_BUS_LOCK_DETECTION;
if (cpu_has_sgx())
opt2 |= SECONDARY_EXEC_ENCLS_EXITING;
if (adjust_vmx_controls(min2, opt2,
@@ -4247,6 +4248,9 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
}
}

+ if (!kvm_bus_lock_exit_enabled(vmx->vcpu.kvm))
+ exec_control &= ~SECONDARY_EXEC_BUS_LOCK_DETECTION;
+
vmx->secondary_exec_control = exec_control;
}

@@ -5661,6 +5665,16 @@ static int handle_encls(struct kvm_vcpu *vcpu)
return 1;
}

+static int handle_bus_lock(struct kvm_vcpu *vcpu)
+{
+ struct kvm_run *kvm_run = vcpu->run;
+
+ vcpu->stat.bus_locks++;
+
+ kvm_run->exit_reason = KVM_EXIT_BUS_LOCK;
+ return 0;
+}
+
/*
* The exit handlers return 1 if the exit was handled fully and guest execution
* may resume. Otherwise they set the kvm_run parameter to indicate what needs
@@ -5717,6 +5731,7 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_VMFUNC] = handle_vmx_instruction,
[EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
[EXIT_REASON_ENCLS] = handle_encls,
+ [EXIT_REASON_BUS_LOCK] = handle_bus_lock,
};

static const int kvm_vmx_max_exit_handlers =
@@ -6809,6 +6824,19 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (unlikely(vmx->exit_reason.failed_vmentry))
return EXIT_FASTPATH_NONE;

+ /*
+ * check the exit_reason to see if there is a bus lock
+ * happened in guest.
+ */
+ if (kvm_bus_lock_exit_enabled(vmx->vcpu.kvm)) {
+ if (vmx->exit_reason.bus_lock_detected) {
+ vcpu->stat.bus_locks++;
+ vcpu->arch.bus_lock_detected = true;
+ } else {
+ vcpu->arch.bus_lock_detected = false;
+ }
+ }
+
vmx->loaded_vmcs->launched = 1;
vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);

@@ -8060,6 +8088,9 @@ static __init int hardware_setup(void)
kvm_tsc_scaling_ratio_frac_bits = 48;
}

+ if (cpu_has_vmx_bus_lock_detection())
+ kvm_has_bus_lock_exit = true;
+
set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */

if (enable_ept)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 06a91b224ef3..7e6d63a8589a 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -104,7 +104,7 @@ union vmx_exit_reason {
u32 reserved23 : 1;
u32 reserved24 : 1;
u32 reserved25 : 1;
- u32 reserved26 : 1;
+ u32 bus_lock_detected : 1;
u32 enclave_mode : 1;
u32 smi_pending_mtf : 1;
u32 smi_from_vmx_root : 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 88c593f83b28..00a54d0cd7da 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -133,6 +133,8 @@ u64 __read_mostly kvm_max_tsc_scaling_ratio;
EXPORT_SYMBOL_GPL(kvm_max_tsc_scaling_ratio);
u64 __read_mostly kvm_default_tsc_scaling_ratio;
EXPORT_SYMBOL_GPL(kvm_default_tsc_scaling_ratio);
+bool __read_mostly kvm_has_bus_lock_exit;
+EXPORT_SYMBOL_GPL(kvm_has_bus_lock_exit);

/* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */
static u32 __read_mostly tsc_tolerance_ppm = 250;
@@ -220,6 +222,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
VCPU_STAT("l1d_flush", l1d_flush),
VCPU_STAT("halt_poll_success_ns", halt_poll_success_ns),
VCPU_STAT("halt_poll_fail_ns", halt_poll_fail_ns),
+ VCPU_STAT("bus_locks", bus_locks),
VM_STAT("mmu_shadow_zapped", mmu_shadow_zapped),
VM_STAT("mmu_pte_write", mmu_pte_write),
VM_STAT("mmu_pte_updated", mmu_pte_updated),
@@ -3538,6 +3541,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
r = kvm_x86_ops.nested_ops->enable_evmcs != NULL;
break;
+ case KVM_CAP_X86_BUS_LOCK_EXIT:
+ r = kvm_has_bus_lock_exit;
+ break;
default:
break;
}
@@ -4990,6 +4996,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.exception_payload_enabled = cap->args[0];
r = 0;
break;
+ case KVM_CAP_X86_BUS_LOCK_EXIT:
+ if (!kvm_has_bus_lock_exit)
+ return -EINVAL;
+ kvm->arch.bus_lock_exit = cap->args[0];
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
@@ -7732,12 +7744,23 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
struct kvm_run *kvm_run = vcpu->run;

kvm_run->if_flag = (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
- kvm_run->flags = is_smm(vcpu) ? KVM_RUN_X86_SMM : 0;
kvm_run->cr8 = kvm_get_cr8(vcpu);
kvm_run->apic_base = kvm_get_apic_base(vcpu);
kvm_run->ready_for_interrupt_injection =
pic_in_kernel(vcpu->kvm) ||
kvm_vcpu_ready_for_interrupt_injection(vcpu);
+
+ if (is_smm(vcpu))
+ kvm_run->flags |= KVM_RUN_X86_SMM;
+ else
+ kvm_run->flags &= ~KVM_RUN_X86_SMM;
+
+ if (vcpu->arch.bus_lock_detected &&
+ kvm_run->exit_reason != KVM_EXIT_BUS_LOCK)
+ kvm_run->flags |= KVM_RUN_BUS_LOCK;
+ else
+ kvm_run->flags &= ~KVM_RUN_BUS_LOCK;
+
}

static void update_cr8_intercept(struct kvm_vcpu *vcpu)
@@ -8597,6 +8620,17 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_lapic_sync_from_vapic(vcpu);

r = kvm_x86_ops.handle_exit(vcpu, exit_fastpath);
+
+ /*
+ * Even when current exit reason is handled by KVM
+ * internally, we still needs to exit to user space
+ * when bus lock detected to inform that there is a
+ * bus lock in guest.
+ */
+ if (r > 0 && vcpu->arch.bus_lock_detected) {
+ vcpu->run->exit_reason = KVM_EXIT_BUS_LOCK;
+ r = 0;
+ }
return r;

cancel_injection:
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 6eb62e97e59f..d3b1095cc8fb 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -334,6 +334,11 @@ static inline bool kvm_cstate_in_guest(struct kvm *kvm)
return kvm->arch.cstate_in_guest;
}

+static inline bool kvm_bus_lock_exit_enabled(struct kvm *kvm)
+{
+ return kvm->arch.bus_lock_exit;
+}
+
DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu);

static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4fdf30316582..e66aa4bdaf24 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -248,6 +248,7 @@ struct kvm_hyperv_exit {
#define KVM_EXIT_IOAPIC_EOI 26
#define KVM_EXIT_HYPERV 27
#define KVM_EXIT_ARM_NISV 28
+#define KVM_EXIT_BUS_LOCK 29

/* For KVM_EXIT_INTERNAL_ERROR */
/* Emulate instruction failed. */
@@ -1031,6 +1032,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_PPC_SECURE_GUEST 181
#define KVM_CAP_HALT_POLL 182
#define KVM_CAP_ASYNC_PF_INT 183
+#define KVM_CAP_X86_BUS_LOCK_EXIT 184

#ifdef KVM_CAP_IRQ_ROUTING

--
2.17.1

Next message: Kuninori Morimoto: "Re: [PATCH v2 0/9] Audio graph card updates and usage with Tegra210 audio"
Previous message: Chenyi Qiang: "[RFC v2 1/2] KVM: VMX: Convert vcpu_vmx.exit_reason to a union"
In reply to: Chenyi Qiang: "[RFC v2 1/2] KVM: VMX: Convert vcpu_vmx.exit_reason to a union"
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