[PATCH 05/15] perf: Track guest callbacks on a per-CPU basis
From: Sean Christopherson
Date: Thu Aug 26 2021 - 20:58:00 EST
Use a per-CPU pointer to track perf's guest callbacks so that KVM can set
the callbacks more precisely and avoid a lurking NULL pointer dereference.
On x86, KVM supports being built as a module and thus can be unloaded.
And because the shared callbacks are referenced from IRQ/NMI context,
unloading KVM can run concurrently with perf, and thus all of perf's
checks for a NULL perf_guest_cbs are flawed as perf_guest_cbs could be
nullified between the check and dereference.
In practice, this has not been problematic because the callbacks are
always guarded with a "perf_guest_cbs && perf_guest_cbs->is_in_guest()"
pattern, and it's extremely unlikely the compiler will choost to reload
perf_guest_cbs in that particular sequence. Because is_in_guest() is
obviously true only when KVM is running a guest, perf always wins the
race to the guarded code (which does often reload perf_guest_cbs) as KVM
has to stop running all guests and do a heavy teardown before unloading.
Cc: Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/arm64/kernel/perf_callchain.c | 18 ++++++++++++------
arch/x86/events/core.c | 17 +++++++++++------
arch/x86/events/intel/core.c | 8 +++++---
include/linux/perf_event.h | 2 +-
kernel/events/core.c | 12 +++++++++---
5 files changed, 38 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 4a72c2727309..38555275c6a2 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -102,7 +102,9 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
struct pt_regs *regs)
{
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
+
+ if (guest_cbs && guest_cbs->is_in_guest()) {
/* We don't support guest os callchain now */
return;
}
@@ -147,9 +149,10 @@ static bool callchain_trace(void *data, unsigned long pc)
void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
struct pt_regs *regs)
{
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
struct stackframe frame;
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+ if (guest_cbs && guest_cbs->is_in_guest()) {
/* We don't support guest os callchain now */
return;
}
@@ -160,18 +163,21 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
unsigned long perf_instruction_pointer(struct pt_regs *regs)
{
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
- return perf_guest_cbs->get_guest_ip();
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
+
+ if (guest_cbs && guest_cbs->is_in_guest())
+ return guest_cbs->get_guest_ip();
return instruction_pointer(regs);
}
unsigned long perf_misc_flags(struct pt_regs *regs)
{
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
int misc = 0;
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
- if (perf_guest_cbs->is_user_mode())
+ if (guest_cbs && guest_cbs->is_in_guest()) {
+ if (guest_cbs->is_user_mode())
misc |= PERF_RECORD_MISC_GUEST_USER;
else
misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 1eb45139fcc6..34155a52e498 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2761,10 +2761,11 @@ static bool perf_hw_regs(struct pt_regs *regs)
void
perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
struct unwind_state state;
unsigned long addr;
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+ if (guest_cbs && guest_cbs->is_in_guest()) {
/* TODO: We don't support guest os callchain now */
return;
}
@@ -2864,10 +2865,11 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
void
perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
struct stack_frame frame;
const struct stack_frame __user *fp;
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+ if (guest_cbs && guest_cbs->is_in_guest()) {
/* TODO: We don't support guest os callchain now */
return;
}
@@ -2944,18 +2946,21 @@ static unsigned long code_segment_base(struct pt_regs *regs)
unsigned long perf_instruction_pointer(struct pt_regs *regs)
{
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
- return perf_guest_cbs->get_guest_ip();
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
+
+ if (guest_cbs && guest_cbs->is_in_guest())
+ return guest_cbs->get_guest_ip();
return regs->ip + code_segment_base(regs);
}
unsigned long perf_misc_flags(struct pt_regs *regs)
{
+ struct perf_guest_info_callbacks *guest_cbs = this_cpu_read(perf_guest_cbs);
int misc = 0;
- if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
- if (perf_guest_cbs->is_user_mode())
+ if (guest_cbs && guest_cbs->is_in_guest()) {
+ if (guest_cbs->is_user_mode())
misc |= PERF_RECORD_MISC_GUEST_USER;
else
misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index fca7a6e2242f..96001962c24d 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2784,6 +2784,7 @@ static void intel_pmu_reset(void)
static int handle_pmi_common(struct pt_regs *regs, u64 status)
{
+ struct perf_guest_info_callbacks *guest_cbs;
struct perf_sample_data data;
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
int bit;
@@ -2852,9 +2853,10 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
*/
if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
handled++;
- if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() &&
- perf_guest_cbs->handle_intel_pt_intr))
- perf_guest_cbs->handle_intel_pt_intr();
+ guest_cbs = this_cpu_read(perf_guest_cbs);
+ if (unlikely(guest_cbs && guest_cbs->is_in_guest() &&
+ guest_cbs->handle_intel_pt_intr))
+ guest_cbs->handle_intel_pt_intr();
else
intel_pt_interrupt();
}
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5eab690622ca..c98253dae037 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1237,7 +1237,7 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
u16 flags);
#ifdef CONFIG_HAVE_GUEST_PERF_EVENTS
-extern struct perf_guest_info_callbacks *perf_guest_cbs;
+DECLARE_PER_CPU(struct perf_guest_info_callbacks *, perf_guest_cbs);
extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
extern void perf_unregister_guest_info_callbacks(void);
#endif /* CONFIG_HAVE_GUEST_PERF_EVENTS */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9820df7ee455..9bc1375d6ed9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6483,17 +6483,23 @@ static void perf_pending_event(struct irq_work *entry)
}
#ifdef CONFIG_HAVE_GUEST_PERF_EVENTS
-struct perf_guest_info_callbacks *perf_guest_cbs;
+DEFINE_PER_CPU(struct perf_guest_info_callbacks *, perf_guest_cbs);
void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
{
- perf_guest_cbs = cbs;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(perf_guest_cbs, cpu) = cbs;
}
EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
void perf_unregister_guest_info_callbacks(void)
{
- perf_guest_cbs = NULL;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(perf_guest_cbs, cpu) = NULL;
}
EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
#endif
--
2.33.0.259.gc128427fd7-goog