From: Kan Liang <kan.li...@intel.com>
x86, perf: Protect LBR and extra_regs against KVM lying
With -cpu host, KVM reports LBR and extra_regs support, if the host has
support.
When the guest perf driver tries to access LBR or extra_regs MSR,
it #GPs all MSR accesses,since KVM doesn't handle LBR and extra_regs support.
So check the related MSRs access right once at initialization time to avoid
the error access at runtime.
For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y
(for host kernel).
And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
Start the guest with -cpu host.
Run perf record with --branch-any or --branch-filter in guest to trigger LBR
Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest to
trigger offcore_rsp #GP
Signed-off-by: Kan Liang <kan.li...@intel.com>
---
V2: Move the check code to initialization time.
V3: Add flag for each extra register.
Check all LBR MSRs at initialization time.
V4: Remove lbr_msr_access.
For LBR msr, simply set lbr_nr to 0 if check_msr failed.
Disable all extra msrs in creation places if check_msr failed.
V5: Fix check_msr broken
Don't check any more MSRs after the first fail
Return error when checking fail to stop creating the event
Remove the checking code path which never get
V6: Move extra_msr_access to struct extra_reg
Modify and move check_msr function to perf_event_intel.c
Other minor code changes
arch/x86/kernel/cpu/perf_event.c | 3 ++
arch/x86/kernel/cpu/perf_event.h | 20 ++++----
arch/x86/kernel/cpu/perf_event_intel.c | 66 ++++++++++++++++++++++++++-
arch/x86/kernel/cpu/perf_event_intel_uncore.h | 4 +-
4 files changed, 81 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 2bdfbff..2879ecd 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -118,6 +118,9 @@ static int x86_pmu_extra_regs(u64 config, struct perf_event
*event)
continue;
if (event->attr.config1 & ~er->valid_mask)
return -EINVAL;
+ /* Check if the extra msrs can be safely accessed*/
+ if (!er->extra_msr_access)
+ return -ENXIO;
reg->idx = er->idx;
reg->config = event->attr.config1;
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 3b2f9bd..2e613b2 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -295,22 +295,24 @@ struct extra_reg {
u64 config_mask;
u64 valid_mask;
int idx; /* per_xxx->regs[] reg index */
+ bool extra_msr_access;
};
-#define EVENT_EXTRA_REG(e, ms, m, vm, i) { \
- .event = (e), \
- .msr = (ms), \
- .config_mask = (m), \
- .valid_mask = (vm), \
- .idx = EXTRA_REG_##i, \
+#define EVENT_EXTRA_REG(e, ms, m, vm, i, a) { \
+ .event = (e), \
+ .msr = (ms), \
+ .config_mask = (m), \
+ .valid_mask = (vm), \
+ .idx = EXTRA_REG_##i, \
+ .extra_msr_access = (a), \
}
#define INTEL_EVENT_EXTRA_REG(event, msr, vm, idx) \
- EVENT_EXTRA_REG(event, msr, ARCH_PERFMON_EVENTSEL_EVENT, vm, idx)
+ EVENT_EXTRA_REG(event, msr, ARCH_PERFMON_EVENTSEL_EVENT, vm, idx, true)
#define INTEL_UEVENT_EXTRA_REG(event, msr, vm, idx) \
EVENT_EXTRA_REG(event, msr, ARCH_PERFMON_EVENTSEL_EVENT | \
- ARCH_PERFMON_EVENTSEL_UMASK, vm, idx)
+ ARCH_PERFMON_EVENTSEL_UMASK, vm, idx, true)
#define INTEL_UEVENT_PEBS_LDLAT_EXTRA_REG(c) \
INTEL_UEVENT_EXTRA_REG(c, \
@@ -318,7 +320,7 @@ struct extra_reg {
0xffff, \
LDLAT)
-#define EVENT_EXTRA_END EVENT_EXTRA_REG(0, 0, 0, 0, RSP_0)
+#define EVENT_EXTRA_END EVENT_EXTRA_REG(0, 0, 0, 0, RSP_0, false)
union perf_capabilities {
struct {
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
b/arch/x86/kernel/cpu/perf_event_intel.c
index adb02aa..9c234d1 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2173,6 +2173,40 @@ static void intel_snb_check_microcode(void)
}
}
+/*
+ * Under certain circumstances, access certain MSR may cause #GP.
+ * The function tests if the input MSR can be safely accessed.
+ */
+static bool check_msr(unsigned long msr, u64 mask)
+{
+ u64 val_old, val_new, val_tmp;
+
+ /*
+ * Read the current value, change it and read it back to see if it
+ * matches, this is needed to detect certain hardware emulators
+ * (qemu/kvm) that don't trap on the MSR access and always return 0s.
+ */
+ if (rdmsrl_safe(msr, &val_old))
+ return false;
+ /*
+ * Only chagne the bits which can be updated by wrmsrl.
+ */
+ val_tmp = val_old ^ mask;
+ if (wrmsrl_safe(msr, val_tmp) ||
+ rdmsrl_safe(msr, &val_new))
+ return false;
+
+ if (val_new != val_tmp)
+ return false;
+
+ /* Here it's sure that the MSR can be safely accessed.
+ * Restore the old value and return.
+ */
+ wrmsrl(msr, val_old);
+
+ return true;
+}
+
static __init void intel_sandybridge_quirk(void)
{
x86_pmu.check_microcode = intel_snb_check_microcode;
@@ -2262,7 +2296,8 @@ __init int intel_pmu_init(void)
union cpuid10_ebx ebx;
struct event_constraint *c;
unsigned int unused;
- int version;
+ int version, i;
+ struct extra_reg *er;
if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
switch (boot_cpu_data.x86) {
@@ -2565,6 +2600,35 @@ __init int intel_pmu_init(void)
}
}
+ /*
+ * Access LBR MSR may cause #GP under certain circumstances.
+ * E.g. KVM doesn't support LBR MSR
+ * Check all LBT MSR here.
+ * Disable LBR access if any LBR MSRs can not be accessed.
+ */
+ if (x86_pmu.lbr_nr && !check_msr(x86_pmu.lbr_tos, 0x3UL))
+ x86_pmu.lbr_nr = 0;
+ for (i = 0; i < x86_pmu.lbr_nr; i++) {
+ if (!(check_msr(x86_pmu.lbr_from + i, 0xffffUL) &&
+ check_msr(x86_pmu.lbr_to + i, 0xffffUL)))
+ x86_pmu.lbr_nr = 0;
+ }
+ /*
+ * Access extra MSR may cause #GP under certain circumstances.
+ * E.g. KVM doesn't support offcore event
+ * Check all extra_regs here.
+ */
+ if (x86_pmu.extra_regs) {
+ for (er = x86_pmu.extra_regs; er->msr; er++) {
+ er->extra_msr_access =
+ check_msr(er->msr, 0x1ffUL);
+ /* Disable LBR select mapping */
+ if ((er->idx == EXTRA_REG_LBR) &&
+ !er->extra_msr_access)
+ x86_pmu.lbr_sel_map = NULL;
+ }
+ }
+
/* Support full width counters using alternative MSR range */
if (x86_pmu.intel_cap.full_width_write) {
x86_pmu.max_period = x86_pmu.cntval_mask;
diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.h
b/arch/x86/kernel/cpu/perf_event_intel_uncore.h
index 90236f0..d860e26 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_uncore.h
+++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.h
@@ -366,11 +366,11 @@
NHMEX_M_PMON_CTL_FLAG_MODE)
#define MBOX_INC_SEL_EXTAR_REG(c, r) \
EVENT_EXTRA_REG(MBOX_INC_SEL(c), NHMEX_M0_MSR_PMU_##r, \
- MBOX_INC_SEL_MASK, (u64)-1, NHMEX_M_##r)
+ MBOX_INC_SEL_MASK, (u64)-1, NHMEX_M_##r, true)
#define MBOX_SET_FLAG_SEL_EXTRA_REG(c, r) \
EVENT_EXTRA_REG(MBOX_SET_FLAG_SEL(c), NHMEX_M0_MSR_PMU_##r, \
MBOX_SET_FLAG_SEL_MASK, \
- (u64)-1, NHMEX_M_##r)
+ (u64)-1, NHMEX_M_##r, true)
/* NHM-EX Rbox */
#define NHMEX_R_MSR_GLOBAL_CTL 0xe00
--
1.8.3.1
--
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