[PATCH] x86, fpu: add tracepoints to dump FPU state at key points

From: Dave Hansen
Date: Wed Jun 01 2016 - 13:42:25 EST


I posted this a few months ago, and Ingo sounded like he'd be
willing to merge this. So here goes.

--
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

I've been carrying this patch around for a bit and it's helped me
solve at least a couple FPU-related bugs. In addition to using
it for debugging, I also drug it out because using AVX (and
AVX2/AVX-512) can have serious power consequences for a modern
core. It's very important to be able to figure out who is using
it.

It's also insanely useful to go out and see who is using a given
feature, like MPX or Memory Protection Keys. If you, for
instance, want to find all processes using protection keys, you
can do:

echo 'xfeatures & 0x200' > filter

Since 0x200 is the protection keys feature bit.

Note that this touches the KVM code. KVM did a CREATE_TRACE_POINTS
and then included a bunch of random headers. If anyone one of
those included other tracepoints, it would have defined the *OTHER*
tracepoints. That's bogus, so move it to the right place.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
---

b/arch/x86/include/asm/fpu/internal.h | 5 +
b/arch/x86/include/asm/trace/fpu.h | 119 ++++++++++++++++++++++++++++++++++
b/arch/x86/kernel/fpu/core.c | 18 +++++
b/arch/x86/kernel/fpu/signal.c | 3
b/arch/x86/kvm/x86.c | 6 -
5 files changed, 148 insertions(+), 3 deletions(-)

diff -puN arch/x86/include/asm/fpu/internal.h~fpu-trace-v1 arch/x86/include/asm/fpu/internal.h
--- a/arch/x86/include/asm/fpu/internal.h~fpu-trace-v1 2016-06-01 10:35:58.216193182 -0700
+++ b/arch/x86/include/asm/fpu/internal.h 2016-06-01 10:35:58.231193860 -0700
@@ -18,6 +18,7 @@
#include <asm/fpu/api.h>
#include <asm/fpu/xstate.h>
#include <asm/cpufeature.h>
+#include <asm/trace/fpu.h>

/*
* High level FPU state handling functions:
@@ -524,6 +525,7 @@ static inline void __fpregs_deactivate(s

fpu->fpregs_active = 0;
this_cpu_write(fpu_fpregs_owner_ctx, NULL);
+ trace_x86_fpu_regs_deactivated(fpu);
}

/* Must be paired with a 'clts' (fpregs_activate_hw()) before! */
@@ -533,6 +535,7 @@ static inline void __fpregs_activate(str

fpu->fpregs_active = 1;
this_cpu_write(fpu_fpregs_owner_ctx, fpu);
+ trace_x86_fpu_regs_activated(fpu);
}

/*
@@ -604,11 +607,13 @@ switch_fpu_prepare(struct fpu *old_fpu,

/* But leave fpu_fpregs_owner_ctx! */
old_fpu->fpregs_active = 0;
+ trace_x86_fpu_regs_deactivated(old_fpu);

/* Don't change CR0.TS if we just switch! */
if (fpu.preload) {
new_fpu->counter++;
__fpregs_activate(new_fpu);
+ trace_x86_fpu_regs_activated(new_fpu);
prefetch(&new_fpu->state);
} else {
__fpregs_deactivate_hw();
diff -puN arch/x86/include/asm/trace/fpu.h~fpu-trace-v1 arch/x86/include/asm/trace/fpu.h
--- a/arch/x86/include/asm/trace/fpu.h~fpu-trace-v1 2016-06-01 10:35:58.219193317 -0700
+++ b/arch/x86/include/asm/trace/fpu.h 2016-06-01 10:35:58.231193860 -0700
@@ -0,0 +1,119 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM x86_fpu
+
+#if !defined(_TRACE_FPU_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_FPU_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(x86_fpu,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu),
+
+ TP_STRUCT__entry(
+ __field(struct fpu *, fpu)
+ __field(bool, fpregs_active)
+ __field(bool, fpstate_active)
+ __field(int, counter)
+ __field(u64, xfeatures)
+ __field(u64, xcomp_bv)
+ ),
+
+ TP_fast_assign(
+ __entry->fpu = fpu;
+ __entry->fpregs_active = fpu->fpregs_active;
+ __entry->fpstate_active = fpu->fpstate_active;
+ __entry->counter = fpu->counter;
+ if (boot_cpu_has(X86_FEATURE_OSXSAVE)) {
+ __entry->xfeatures = fpu->state.xsave.header.xfeatures;
+ __entry->xcomp_bv = fpu->state.xsave.header.xcomp_bv;
+ }
+ ),
+ TP_printk("x86/fpu: %p fpregs_active: %d fpstate_active: %d counter: %d xfeatures: %llx xcomp_bv: %llx",
+ __entry->fpu,
+ __entry->fpregs_active,
+ __entry->fpstate_active,
+ __entry->counter,
+ __entry->xfeatures,
+ __entry->xcomp_bv
+ )
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_state,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_before_save,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_after_save,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_before_restore,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_after_restore,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_regs_activated,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_regs_deactivated,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_activate_state,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_deactivate_state,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_init_state,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_dropped,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_copy_src,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_copy_dst,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+DEFINE_EVENT(x86_fpu, x86_fpu_xstate_check_failed,
+ TP_PROTO(struct fpu *fpu),
+ TP_ARGS(fpu)
+);
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH asm/trace/
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE fpu
+#endif /* _TRACE_FPU_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff -puN arch/x86/kernel/fpu/core.c~fpu-trace-v1 arch/x86/kernel/fpu/core.c
--- a/arch/x86/kernel/fpu/core.c~fpu-trace-v1 2016-06-01 10:35:58.221193408 -0700
+++ b/arch/x86/kernel/fpu/core.c 2016-06-01 10:35:58.232193905 -0700
@@ -12,6 +12,9 @@

#include <linux/hardirq.h>

+#define CREATE_TRACE_POINTS
+#include <asm/trace/fpu.h>
+
/*
* Represents the initial FPU state. It's mostly (but not completely) zeroes,
* depending on the FPU hardware format:
@@ -192,6 +195,7 @@ void fpu__save(struct fpu *fpu)
WARN_ON_FPU(fpu != &current->thread.fpu);

preempt_disable();
+ trace_x86_fpu_before_save(fpu);
if (fpu->fpregs_active) {
if (!copy_fpregs_to_fpstate(fpu)) {
if (use_eager_fpu())
@@ -200,6 +204,7 @@ void fpu__save(struct fpu *fpu)
fpregs_deactivate(fpu);
}
}
+ trace_x86_fpu_after_save(fpu);
preempt_enable();
}
EXPORT_SYMBOL_GPL(fpu__save);
@@ -275,6 +280,9 @@ int fpu__copy(struct fpu *dst_fpu, struc
}
preempt_enable();

+ trace_x86_fpu_copy_src(src_fpu);
+ trace_x86_fpu_copy_dst(dst_fpu);
+
return 0;
}

@@ -288,7 +296,9 @@ void fpu__activate_curr(struct fpu *fpu)

if (!fpu->fpstate_active) {
fpstate_init(&fpu->state);
+ trace_x86_fpu_init_state(fpu);

+ trace_x86_fpu_activate_state(fpu);
/* Safe to do for the current task: */
fpu->fpstate_active = 1;
}
@@ -314,7 +324,9 @@ void fpu__activate_fpstate_read(struct f
} else {
if (!fpu->fpstate_active) {
fpstate_init(&fpu->state);
+ trace_x86_fpu_init_state(fpu);

+ trace_x86_fpu_activate_state(fpu);
/* Safe to do for current and for stopped child tasks: */
fpu->fpstate_active = 1;
}
@@ -347,7 +359,9 @@ void fpu__activate_fpstate_write(struct
fpu->last_cpu = -1;
} else {
fpstate_init(&fpu->state);
+ trace_x86_fpu_init_state(fpu);

+ trace_x86_fpu_activate_state(fpu);
/* Safe to do for stopped child tasks: */
fpu->fpstate_active = 1;
}
@@ -432,9 +446,11 @@ void fpu__restore(struct fpu *fpu)

/* Avoid __kernel_fpu_begin() right after fpregs_activate() */
kernel_fpu_disable();
+ trace_x86_fpu_before_restore(fpu);
fpregs_activate(fpu);
copy_kernel_to_fpregs(&fpu->state);
fpu->counter++;
+ trace_x86_fpu_after_restore(fpu);
kernel_fpu_enable();
}
EXPORT_SYMBOL_GPL(fpu__restore);
@@ -463,6 +479,8 @@ void fpu__drop(struct fpu *fpu)

fpu->fpstate_active = 0;

+ trace_x86_fpu_dropped(fpu);
+
preempt_enable();
}

diff -puN arch/x86/kernel/fpu/signal.c~fpu-trace-v1 arch/x86/kernel/fpu/signal.c
--- a/arch/x86/kernel/fpu/signal.c~fpu-trace-v1 2016-06-01 10:35:58.223193498 -0700
+++ b/arch/x86/kernel/fpu/signal.c 2016-06-01 10:35:58.233193951 -0700
@@ -10,6 +10,7 @@
#include <asm/fpu/regset.h>

#include <asm/sigframe.h>
+#include <asm/trace/fpu.h>

static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;

@@ -282,6 +283,7 @@ static int __fpu__restore_sig(void __use
*/
state_size = sizeof(struct fxregs_state);
fx_only = 1;
+ trace_x86_fpu_xstate_check_failed(fpu);
} else {
state_size = fx_sw_user.xstate_size;
xfeatures = fx_sw_user.xfeatures;
@@ -311,6 +313,7 @@ static int __fpu__restore_sig(void __use
if (__copy_from_user(&fpu->state.xsave, buf_fx, state_size) ||
__copy_from_user(&env, buf, sizeof(env))) {
fpstate_init(&fpu->state);
+ trace_x86_fpu_init_state(fpu);
err = -1;
} else {
sanitize_restored_xstate(tsk, &env, xfeatures, fx_only);
diff -puN arch/x86/kvm/x86.c~fpu-trace-v1 arch/x86/kvm/x86.c
--- a/arch/x86/kvm/x86.c~fpu-trace-v1 2016-06-01 10:35:58.226193634 -0700
+++ b/arch/x86/kvm/x86.c 2016-06-01 10:35:58.237194131 -0700
@@ -55,9 +55,6 @@
#include <linux/irqbypass.h>
#include <trace/events/kvm.h>

-#define CREATE_TRACE_POINTS
-#include "trace.h"
-
#include <asm/debugreg.h>
#include <asm/msr.h>
#include <asm/desc.h>
@@ -68,6 +65,9 @@
#include <asm/div64.h>
#include <asm/irq_remapping.h>

+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
#define MAX_IO_MSRS 256
#define KVM_MAX_MCE_BANKS 32
#define KVM_MCE_CAP_SUPPORTED (MCG_CTL_P | MCG_SER_P)
_