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Message-ID: <87vb3v56x2.fsf@ashishki-desk.ger.corp.intel.com>
Date: Wed, 06 Apr 2016 14:10:49 +0300
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Gleb Natapov <gleb@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
kvm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org, tglx@...utronix.de, hpa@...or.com,
Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH] perf/x86/intel/pt: Don't die on VMXON
Peter Zijlstra <peterz@...radead.org> writes:
> On Fri, Apr 01, 2016 at 07:24:14PM +0300, Alexander Shishkin wrote:
>> +static void pt_config_stop(struct perf_event *event)
>> {
>> + u64 ctl = READ_ONCE(event->hw.config);
>>
>> + /* may be already stopped by a PMI*/
>> + if (!(ctl & RTIT_CTL_TRACEEN))
>> + return;
>> +
>> + ctl ^= RTIT_CTL_TRACEEN;
>
> Would that not be much less confusing when written like |= ?
This one's actually clearing TraceEn, see the if-not-set-leave in front
of it, but that just goes to prove your point I guess. :)
>> +void intel_pt_vmxon(int entry)
>> +{
>> + struct pt *pt = this_cpu_ptr(&pt_ctx);
>> + struct perf_event *event;
>> + unsigned long flags;
>> +
>> + /* PT plays nice with VMX, do nothing */
>> + if (pt_pmu.vmx)
>> + return;
>> +
>> + /*
>> + * VMX entry will clear RTIT_CTL.TraceEn; we need to make
>> + * sure to not try to set it while VMX is on. Disable
>> + * interrupts to avoid racing with pmu callbacks;
>> + * concurrent PMI should be handled fine.
>> + */
>> + local_irq_save(flags);
>> + WRITE_ONCE(pt->vmx_on, entry);
>
> So you mix: "VMX is on" and "VMX entry", please pick one.
>
> Since the function is called vmxon, I find .entry a very confusing
> argument name.
I did struggle with this one indeed.
How about this then:
>From 9faf95f173decda1f2e3101ced9d9370c14f2339 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Date: Tue, 29 Mar 2016 17:43:10 +0300
Subject: [PATCH] perf/x86/intel/pt: Don't die on VMXON
Some versions of Intel PT do not support tracing across VMXON, more
specifically, VMXON will clear TraceEn control bit and any attempt to
set it before VMXOFF will throw a #GP, which in the current state of
things will crash the kernel. Namely,
$ perf record -e intel_pt// kvm -nographic
on such a machine will kill it.
To avoid this, notify the intel_pt driver before VMXON and after
VMXOFF so that it knows when not to enable itself.
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
arch/x86/events/intel/pt.c | 71 +++++++++++++++++++++++++++++++++------
arch/x86/events/intel/pt.h | 2 ++
arch/x86/include/asm/perf_event.h | 4 +++
arch/x86/kvm/vmx.c | 4 +++
4 files changed, 70 insertions(+), 11 deletions(-)
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 127f58c179..02384cc6ff 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -136,9 +136,17 @@ static int __init pt_pmu_hw_init(void)
struct dev_ext_attribute *de_attrs;
struct attribute **attrs;
size_t size;
+ u64 reg;
int ret;
long i;
+ if (test_cpu_cap(&boot_cpu_data, X86_FEATURE_VMX)) {
+ /* Intel SDM, 36.5 "Tracing post-VMXON" */
+ rdmsrl(MSR_IA32_VMX_MISC, reg);
+ if (reg & BIT(14))
+ pt_pmu.vmx = true;
+ }
+
attrs = NULL;
for (i = 0; i < PT_CPUID_LEAVES; i++) {
@@ -269,20 +277,23 @@ static void pt_config(struct perf_event *event)
reg |= (event->attr.config & PT_CONFIG_MASK);
+ event->hw.config = reg;
wrmsrl(MSR_IA32_RTIT_CTL, reg);
}
-static void pt_config_start(bool start)
+static void pt_config_stop(struct perf_event *event)
{
- u64 ctl;
+ u64 ctl = READ_ONCE(event->hw.config);
- rdmsrl(MSR_IA32_RTIT_CTL, ctl);
- if (start)
- ctl |= RTIT_CTL_TRACEEN;
- else
- ctl &= ~RTIT_CTL_TRACEEN;
+ /* may be already stopped by a PMI */
+ if (!(ctl & RTIT_CTL_TRACEEN))
+ return;
+
+ ctl &= ~RTIT_CTL_TRACEEN;
wrmsrl(MSR_IA32_RTIT_CTL, ctl);
+ WRITE_ONCE(event->hw.config, ctl);
+
/*
* A wrmsr that disables trace generation serializes other PT
* registers and causes all data packets to be written to memory,
@@ -291,8 +302,7 @@ static void pt_config_start(bool start)
* The below WMB, separating data store and aux_head store matches
* the consumer's RMB that separates aux_head load and data load.
*/
- if (!start)
- wmb();
+ wmb();
}
static void pt_config_buffer(void *buf, unsigned int topa_idx,
@@ -922,11 +932,17 @@ void intel_pt_interrupt(void)
if (!ACCESS_ONCE(pt->handle_nmi))
return;
- pt_config_start(false);
+ /*
+ * If VMX is on and PT does not support it, don't touch anything.
+ */
+ if (ACCESS_ONCE(pt->vmx_on))
+ return;
if (!event)
return;
+ pt_config_stop(event);
+
buf = perf_get_aux(&pt->handle);
if (!buf)
return;
@@ -963,6 +979,35 @@ void intel_pt_interrupt(void)
}
}
+void intel_pt_vmx(int on)
+{
+ struct pt *pt = this_cpu_ptr(&pt_ctx);
+ struct perf_event *event;
+ unsigned long flags;
+
+ /* PT plays nice with VMX, do nothing */
+ if (pt_pmu.vmx)
+ return;
+
+ /*
+ * VMXON will clear RTIT_CTL.TraceEn; we need to make
+ * sure to not try to set it while VMX is on. Disable
+ * interrupts to avoid racing with pmu callbacks;
+ * concurrent PMI should be handled fine.
+ */
+ local_irq_save(flags);
+ WRITE_ONCE(pt->vmx_on, on);
+
+ if (on) {
+ /* prevent pt_config_stop() from writing RTIT_CTL */
+ event = pt->handle.event;
+ if (event)
+ event->hw.config = 0;
+ }
+ local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(intel_pt_vmx);
+
/*
* PMU callbacks
*/
@@ -973,6 +1018,9 @@ static void pt_event_start(struct perf_event *event, int mode)
struct pt *pt = this_cpu_ptr(&pt_ctx);
struct pt_buffer *buf;
+ if (ACCESS_ONCE(pt->vmx_on))
+ return;
+
buf = perf_aux_output_begin(&pt->handle, event);
if (!buf)
goto fail_stop;
@@ -1007,7 +1055,8 @@ static void pt_event_stop(struct perf_event *event, int mode)
* see comment in intel_pt_interrupt().
*/
ACCESS_ONCE(pt->handle_nmi) = 0;
- pt_config_start(false);
+
+ pt_config_stop(event);
if (event->hw.state == PERF_HES_STOPPED)
return;
diff --git a/arch/x86/events/intel/pt.h b/arch/x86/events/intel/pt.h
index 336878a5d2..b0731630cd 100644
--- a/arch/x86/events/intel/pt.h
+++ b/arch/x86/events/intel/pt.h
@@ -65,6 +65,7 @@ enum pt_capabilities {
struct pt_pmu {
struct pmu pmu;
u32 caps[PT_CPUID_REGS_NUM * PT_CPUID_LEAVES];
+ bool vmx;
};
/**
@@ -111,6 +112,7 @@ struct pt_buffer {
struct pt {
struct perf_output_handle handle;
int handle_nmi;
+ int vmx_on;
};
#endif /* __INTEL_PT_H__ */
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 5a2ed3ed2f..fcc5956f3f 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -285,6 +285,10 @@ static inline void perf_events_lapic_init(void) { }
static inline void perf_check_microcode(void) { }
#endif
+#ifdef CONFIG_CPU_SUP_INTEL
+ extern void intel_pt_vmx(int on);
+#endif
+
#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
extern void amd_pmu_enable_virt(void);
extern void amd_pmu_disable_virt(void);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1735ae9d68..fa8c98f5fa 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3075,6 +3075,8 @@ static __init int vmx_disabled_by_bios(void)
static void kvm_cpu_vmxon(u64 addr)
{
+ intel_pt_vmx(1);
+
asm volatile (ASM_VMX_VMXON_RAX
: : "a"(&addr), "m"(addr)
: "memory", "cc");
@@ -3144,6 +3146,8 @@ static void vmclear_local_loaded_vmcss(void)
static void kvm_cpu_vmxoff(void)
{
asm volatile (__ex(ASM_VMX_VMXOFF) : : : "cc");
+
+ intel_pt_vmx(0);
}
static void hardware_disable(void)
--
2.8.0.rc3
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