[PATCH v2] KVM: Expose the split lock detection feature to guest VM
From: Jingqi Liu
Date: Wed Jul 04 2018 - 09:07:02 EST
A new control bit(bit 29) in the TEST_CTRL MSR will be introduced
to enable detection of split locks.
When bit 29 of the TEST_CTRL(33H) MSR is set, the processor
causes an #AC exception to be issued instead of suppressing LOCK on
bus(during split lock access). A previous control bit (bit 31)
in this MSR causes the processor to disable LOCK# assertion for
split locked accesses when set. When bits 29 and 31 are both set,
bit 29 takes precedence.
The release document ref below link:
https://software.intel.com/sites/default/files/managed/c5/15/\
architecture-instruction-set-extensions-programming-reference.pdf
This patch has a dependency on https://lkml.org/lkml/2018/5/27/78.
Signed-off-by: Jingqi Liu <jingqi.liu@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/vmx.c | 77 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 10 ++++++
arch/x86/kvm/x86.h | 5 +++
include/uapi/linux/kvm.h | 1 +
5 files changed, 94 insertions(+)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c13cd28..adf4c8e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -809,6 +809,7 @@ struct kvm_arch {
bool mwait_in_guest;
bool hlt_in_guest;
bool pause_in_guest;
+ bool split_lock_ac_in_guest;
unsigned long irq_sources_bitmap;
s64 kvmclock_offset;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1689f43..d380764 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -58,6 +58,9 @@
#include "pmu.h"
#include "vmx_evmcs.h"
+static u64 x86_split_lock_ctrl_base;
+static u64 x86_split_lock_ctrl_mask;
+
#define __ex(x) __kvm_handle_fault_on_reboot(x)
#define __ex_clear(x, reg) \
____kvm_handle_fault_on_reboot(x, "xor " reg " , " reg)
@@ -776,6 +779,7 @@ struct vcpu_vmx {
u64 arch_capabilities;
u64 spec_ctrl;
+ u64 split_lock_ctrl;
u32 vm_entry_controls_shadow;
u32 vm_exit_controls_shadow;
@@ -3750,6 +3754,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
#endif
case MSR_EFER:
return kvm_get_msr_common(vcpu, msr_info);
+ case MSR_TEST_CTL:
+ if (!msr_info->host_initiated &&
+ !kvm_split_lock_ac_in_guest(vcpu->kvm))
+ return 1;
+ msr_info->data = to_vmx(vcpu)->split_lock_ctrl;
+ break;
case MSR_IA32_SPEC_CTRL:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
@@ -3868,6 +3878,19 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
vmcs_write64(GUEST_BNDCFGS, data);
break;
+ case MSR_TEST_CTL:
+ if (!msr_info->host_initiated &&
+ !kvm_split_lock_ac_in_guest(vcpu->kvm))
+ return 1;
+
+ vmx->split_lock_ctrl = data;
+
+ if (!data)
+ break;
+ vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap,
+ MSR_TEST_CTL,
+ MSR_TYPE_RW);
+ break;
case MSR_IA32_SPEC_CTRL:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
@@ -6293,6 +6316,8 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmcs_write64(PML_ADDRESS, page_to_phys(vmx->pml_pg));
vmcs_write16(GUEST_PML_INDEX, PML_ENTITY_NUM - 1);
}
+
+ vmx->split_lock_ctrl = 0;
}
static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
@@ -6303,6 +6328,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
vmx->rmode.vm86_active = 0;
vmx->spec_ctrl = 0;
+ vmx->split_lock_ctrl = 0;
vcpu->arch.microcode_version = 0x100000000ULL;
vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
@@ -9947,6 +9973,38 @@ static void vmx_arm_hv_timer(struct kvm_vcpu *vcpu)
vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, delta_tsc);
}
+static void x86_split_lock_ctrl_init(void)
+{
+ /*
+ * Read the MSR_TEST_CTL MSR to account for reserved bits which may
+ * have unknown values.
+ */
+ if (boot_cpu_has(X86_FEATURE_AC_SPLIT_LOCK)) {
+ rdmsrl(MSR_TEST_CTL, x86_split_lock_ctrl_base);
+ x86_split_lock_ctrl_mask = MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK;
+ }
+}
+
+static void x86_set_split_lock_ctrl(struct kvm_vcpu *vcpu,
+ u64 guest_split_lock_ctrl, bool setguest)
+{
+ /*
+ * Check if the feature of #AC exception
+ * for split locked access is supported.
+ */
+ if (boot_cpu_has(X86_FEATURE_AC_SPLIT_LOCK)) {
+ u64 msrval, guestval;
+ u64 hostval = x86_split_lock_ctrl_base;
+
+ guestval = hostval & ~x86_split_lock_ctrl_mask;
+ guestval |= guest_split_lock_ctrl & x86_split_lock_ctrl_mask;
+ if (hostval != guestval) {
+ msrval = setguest ? guestval : hostval;
+ wrmsrl(MSR_TEST_CTL, msrval);
+ }
+ }
+}
+
static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -10014,6 +10072,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
*/
x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0);
+ /*
+ * Restore the guest's value of TEST_CTL MSR
+ * if it's different with the host's value.
+ */
+ x86_set_split_lock_ctrl(vcpu, vmx->split_lock_ctrl, true);
+
vmx->__launched = vmx->loaded_vmcs->launched;
evmcs_rsp = static_branch_unlikely(&enable_evmcs) ?
@@ -10162,6 +10226,17 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
x86_spec_ctrl_restore_host(vmx->spec_ctrl, 0);
+ if (kvm_split_lock_ac_in_guest(vcpu->kvm) &&
+ !msr_write_intercepted(vcpu, MSR_TEST_CTL)) {
+ vmx->split_lock_ctrl = native_read_msr(MSR_TEST_CTL);
+ }
+
+ /*
+ * Restore the host's value of TEST_CTL MSR
+ * if it's different with the guest's value.
+ */
+ x86_set_split_lock_ctrl(vcpu, vmx->split_lock_ctrl, false);
+
/* Eliminate branch target predictions from guest mode */
vmexit_fill_RSB();
@@ -13120,6 +13195,8 @@ static int __init vmx_init(void)
{
int r;
+ x86_split_lock_ctrl_init();
+
#if IS_ENABLED(CONFIG_HYPERV)
/*
* Enlightened VMCS usage should be recommended and the host needs
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0046aa7..2611022 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2942,6 +2942,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_X2APIC_API:
r = KVM_X2APIC_API_VALID_FLAGS;
break;
+ case KVM_CAP_X86_SPLIT_LOCK_AC:
+ if (boot_cpu_has(X86_FEATURE_AC_SPLIT_LOCK))
+ r = 1;
+ else
+ r = 0;
+ break;
default:
break;
}
@@ -4260,6 +4266,10 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.pause_in_guest = true;
r = 0;
break;
+ case KVM_CAP_X86_SPLIT_LOCK_AC:
+ kvm->arch.split_lock_ac_in_guest = true;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 257f276..aa4daeb 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -326,6 +326,11 @@ static inline bool kvm_pause_in_guest(struct kvm *kvm)
return kvm->arch.pause_in_guest;
}
+static inline bool kvm_split_lock_ac_in_guest(struct kvm *kvm)
+{
+ return kvm->arch.split_lock_ac_in_guest;
+}
+
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 b6270a3..219f5fd 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -949,6 +949,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_GET_MSR_FEATURES 153
#define KVM_CAP_HYPERV_EVENTFD 154
#define KVM_CAP_HYPERV_TLBFLUSH 155
+#define KVM_CAP_X86_SPLIT_LOCK_AC 156
#ifdef KVM_CAP_IRQ_ROUTING
--
1.8.3.1