Re: [PATCH v7 05/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest Arch LBR

From: Like Xu
Date: Mon Aug 09 2021 - 09:37:02 EST

On 6/8/2021 3:42 pm, Yang Weijiang wrote:
From: Like Xu <like.xu@xxxxxxxxxxxxxxx>

Arch LBRs are enabled by setting MSR_ARCH_LBR_CTL.LBREn to 1. A new guest
state field named "Guest IA32_LBR_CTL" is added to enhance guest LBR usage.
When guest Arch LBR is enabled, a guest LBR event will be created like the
model-specific LBR does. Clear guest LBR enable bit on host PMI handling so
guest can see expected config.

On processors that support Arch LBR, MSR_IA32_DEBUGCTLMSR[bit 0] has no
meaning. It can be written to 0 or 1, but reads will always return 0.
Like IA32_DEBUGCTL, IA32_ARCH_LBR_CTL msr is also preserved on INIT.

Regardless of the Arch LBR or legacy LBR, when the LBR_EN bit 0 of the
corresponding control MSR is set to 1, LBR recording will be enabled.

Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/events/intel/lbr.c | 2 --
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/include/asm/vmx.h | 2 ++
arch/x86/kvm/vmx/pmu_intel.c | 48 ++++++++++++++++++++++++++++----
arch/x86/kvm/vmx/vmx.c | 9 ++++++
5 files changed, 55 insertions(+), 7 deletions(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index ceff16eb4bcb..d6773a200c70 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -168,8 +168,6 @@ enum {
ARCH_LBR_RETURN |\
ARCH_LBR_OTHER_BRANCH)
-#define ARCH_LBR_CTL_MASK 0x7f000e
-
static void intel_pmu_lbr_filter(struct cpu_hw_events *cpuc);
static __always_inline bool is_lbr_call_stack_bit_set(u64 config)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index a7c413432b33..04059e8ed115 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -169,6 +169,7 @@
#define LBR_INFO_BR_TYPE (0xfull << LBR_INFO_BR_TYPE_OFFSET)
#define MSR_ARCH_LBR_CTL 0x000014ce
+#define ARCH_LBR_CTL_MASK 0x7f000e
#define ARCH_LBR_CTL_LBREN BIT(0)
#define ARCH_LBR_CTL_CPL_OFFSET 1
#define ARCH_LBR_CTL_CPL (0x3ull << ARCH_LBR_CTL_CPL_OFFSET)
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 0ffaa3156a4e..ea3be961cc8e 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -245,6 +245,8 @@ enum vmcs_field {
GUEST_BNDCFGS_HIGH = 0x00002813,
GUEST_IA32_RTIT_CTL = 0x00002814,
GUEST_IA32_RTIT_CTL_HIGH = 0x00002815,
+ GUEST_IA32_LBR_CTL = 0x00002816,
+ GUEST_IA32_LBR_CTL_HIGH = 0x00002817,
HOST_IA32_PAT = 0x00002c00,
HOST_IA32_PAT_HIGH = 0x00002c01,
HOST_IA32_EFER = 0x00002c02,
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index a4ef5bbce186..b2631fea5e6c 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -19,6 +19,7 @@
#include "pmu.h"
#define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)
+#define KVM_ARCH_LBR_CTL_MASK (ARCH_LBR_CTL_MASK | ARCH_LBR_CTL_LBREN)
static struct kvm_event_hw_type_mapping intel_arch_events[] = {
/* Index must match CPUID 0x0A.EBX bit vector */
@@ -221,6 +222,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
ret = pmu->version > 1;
break;
case MSR_ARCH_LBR_DEPTH:
+ case MSR_ARCH_LBR_CTL:
if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
ret = guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR);
break;
@@ -369,6 +371,26 @@ static bool arch_lbr_depth_is_valid(struct kvm_vcpu *vcpu, u64 depth)
return (depth == fls(eax & 0xff) * 8);
}
+#define ARCH_LBR_CTL_BRN_MASK GENMASK_ULL(22, 16)
+
+static bool arch_lbr_ctl_is_valid(struct kvm_vcpu *vcpu, u64 ctl)
+{
+ unsigned int eax, ebx, ecx, edx;
+
+ if (!kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
+ return false;
+
+ cpuid_count(0x1c, 0, &eax, &ebx, &ecx, &edx);
+ if (!(ebx & BIT(0)) && (ctl & ARCH_LBR_CTL_CPL))
+ return false;
+ if (!(ebx & BIT(2)) && (ctl & ARCH_LBR_CTL_STACK))
+ return false;
+ if (!(ebx & BIT(1)) && (ctl & ARCH_LBR_CTL_BRN_MASK))
+ return false;
+
+ return !(ctl & ~KVM_ARCH_LBR_CTL_MASK);
+}

Please check it with the *guest* cpuid entry.

And it should remove the bits that are not supported by x86_pmu.lbr_ctl_mask before
vmcs_write64(...) if the guest value is a superset of the host value with warning message.

+
static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
@@ -392,6 +414,9 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
case MSR_ARCH_LBR_DEPTH:
msr_info->data = lbr_desc->records.nr;
return 0;
+ case MSR_ARCH_LBR_CTL:
+ msr_info->data = vmcs_read64(GUEST_IA32_LBR_CTL);
+ return 0;
default:
if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
(pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
@@ -460,6 +485,15 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (!msr_info->host_initiated)
wrmsrl(MSR_ARCH_LBR_DEPTH, lbr_desc->records.nr);
return 0;
+ case MSR_ARCH_LBR_CTL:
+ if (!arch_lbr_ctl_is_valid(vcpu, data))
+ break;
+
+ vmcs_write64(GUEST_IA32_LBR_CTL, data);
+ if (intel_pmu_lbr_is_enabled(vcpu) && !lbr_desc->event &&
+ (data & ARCH_LBR_CTL_LBREN))
+ intel_pmu_create_guest_lbr_event(vcpu);
+ return 0;
default:
if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
(pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
@@ -637,12 +671,16 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu)
*/
static void intel_pmu_legacy_freezing_lbrs_on_pmi(struct kvm_vcpu *vcpu)
{
- u64 data = vmcs_read64(GUEST_IA32_DEBUGCTL);
+ u32 lbr_ctl_field = GUEST_IA32_DEBUGCTL;
- if (data & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI) {
- data &= ~DEBUGCTLMSR_LBR;
- vmcs_write64(GUEST_IA32_DEBUGCTL, data);
- }
+ if (!(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI))
+ return;
+
+ if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
+ guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
+ lbr_ctl_field = GUEST_IA32_LBR_CTL;
+
+ vmcs_write64(lbr_ctl_field, vmcs_read64(lbr_ctl_field) & ~0x1ULL);
}
static void intel_pmu_deliver_pmi(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 927a552393b9..e8df44faf900 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2002,6 +2002,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
VM_EXIT_SAVE_DEBUG_CONTROLS)
get_vmcs12(vcpu)->guest_ia32_debugctl = data;
+ /*
+ * For Arch LBR, IA32_DEBUGCTL[bit 0] has no meaning.
+ * It can be written to 0 or 1, but reads will always return 0.
+ */
+ if (guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
+ data &= ~DEBUGCTLMSR_LBR;
+
vmcs_write64(GUEST_IA32_DEBUGCTL, data);
if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event &&
(data & DEBUGCTLMSR_LBR))
@@ -4441,6 +4448,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
vmcs_writel(GUEST_SYSENTER_ESP, 0);
vmcs_writel(GUEST_SYSENTER_EIP, 0);
vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
+ if (static_cpu_has(X86_FEATURE_ARCH_LBR))
+ vmcs_write64(GUEST_IA32_LBR_CTL, 0);

Please update dump_vmcs() to dump GUEST_IA32_LBR_CTL as well.

How about update the load_vmcs12_host_state() for GUEST_IA32_LBR_CTL
since you enabled the nested case in this patch set ?

}
kvm_set_rflags(vcpu, X86_EFLAGS_FIXED);