Skip to content

Commit

Permalink
x86/fpu: Add tracepoints to dump FPU state at key points
Browse files Browse the repository at this point in the history 
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@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160601174220.3CDFB90E@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
  • Loading branch information
Dave Hansen authored and Ingo Molnar committed Jun 8, 2016
1 parent c8ae067 commit d1898b7
Show file tree
Hide file tree
Showing 5 changed files with 148 additions and 3 deletions.
5 changes: 5 additions & 0 deletions arch/x86/include/asm/fpu/internal.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand Down Expand Up @@ -524,6 +525,7 @@ static inline void __fpregs_deactivate(struct fpu *fpu)

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! */
Expand All @@ -533,6 +535,7 @@ static inline void __fpregs_activate(struct fpu *fpu)

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

/*
Expand Down Expand Up @@ -604,11 +607,13 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu)

/* 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();
Expand Down
119 changes: 119 additions & 0 deletions arch/x86/include/asm/trace/fpu.h
View file
Original file line number Diff line number Diff line change
@@ -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>
18 changes: 18 additions & 0 deletions arch/x86/kernel/fpu/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand Down Expand Up @@ -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())
Expand All @@ -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);
Expand Down Expand Up @@ -275,6 +280,9 @@ int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
}
preempt_enable();

trace_x86_fpu_copy_src(src_fpu);
trace_x86_fpu_copy_dst(dst_fpu);

return 0;
}

Expand All @@ -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;
}
Expand All @@ -314,7 +324,9 @@ void fpu__activate_fpstate_read(struct fpu *fpu)
} 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;
}
Expand Down Expand Up @@ -347,7 +359,9 @@ void fpu__activate_fpstate_write(struct fpu *fpu)
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;
}
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -463,6 +479,8 @@ void fpu__drop(struct fpu *fpu)

fpu->fpstate_active = 0;

trace_x86_fpu_dropped(fpu);

preempt_enable();
}

Expand Down
3 changes: 3 additions & 0 deletions arch/x86/kernel/fpu/signal.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -282,6 +283,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
*/
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;
Expand Down Expand Up @@ -311,6 +313,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
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);
Expand Down
6 changes: 3 additions & 3 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -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)
Expand Down

0 comments on commit d1898b7

Please sign in to comment.