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Date: Tue, 11 May 2021 13:59:40 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Rob Herring <robh@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andi Kleen <ak@...ux.intel.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Andy Lutomirski <luto@...capital.net>,
Stephane Eranian <eranian@...gle.com>,
Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH V6] perf: Reset the dirty counter to prevent the leak for
an RDPMC task
On 5/10/2021 4:29 PM, Rob Herring wrote:
> On Mon, May 10, 2021 at 2:18 PM Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> On Thu, Apr 22, 2021 at 11:25:52AM -0700, kan.liang@...ux.intel.com wrote:
>>
>>> - Add a new method check_leakage() to check and clear dirty counters
>>> to prevent potential leakage.
>>
>> I really dislike adding spurious callbacks, also because indirect calls
>> are teh suck, but also because it pollutes the interface so.
>>
>> That said, I'm not sure I actually like the below any better :/
>>
Maybe we can add a atomic variable to track the number of
event_mapped(). Only invoke sched_task() when the number > 0.
It looks like only X86 implements the event_mapped(). So it should not
impact other ARCHs.
What do you think?
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index c6fedd2..ae5b0e7 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1636,6 +1636,8 @@ static void x86_pmu_del(struct perf_event *event,
int flags)
if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
goto do_del;
+ __set_bit(event->hw.idx, cpuc->dirty);
+
/*
* Not a TXN, therefore cleanup properly.
*/
@@ -2484,6 +2486,31 @@ static int x86_pmu_event_init(struct perf_event
*event)
return err;
}
+static void x86_pmu_clear_dirty_counters(void)
+{
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ int i;
+
+ /* Don't need to clear the assigned counter. */
+ for (i = 0; i < cpuc->n_events; i++)
+ __clear_bit(cpuc->assign[i], cpuc->dirty);
+
+ if (bitmap_empty(cpuc->dirty, X86_PMC_IDX_MAX))
+ return;
+
+ for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) {
+ /* Metrics and fake events don't have corresponding HW counters. */
+ if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR))
+ continue;
+ else if (i >= INTEL_PMC_IDX_FIXED)
+ wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + (i - INTEL_PMC_IDX_FIXED), 0);
+ else
+ wrmsrl(x86_pmu_event_addr(i), 0);
+ }
+
+ bitmap_zero(cpuc->dirty, X86_PMC_IDX_MAX);
+}
+
static void x86_pmu_event_mapped(struct perf_event *event, struct
mm_struct *mm)
{
if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
@@ -2507,7 +2534,6 @@ static void x86_pmu_event_mapped(struct perf_event
*event, struct mm_struct *mm)
static void x86_pmu_event_unmapped(struct perf_event *event, struct
mm_struct *mm)
{
-
if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return;
@@ -2616,6 +2642,14 @@ static const struct attribute_group
*x86_pmu_attr_groups[] = {
static void x86_pmu_sched_task(struct perf_event_context *ctx, bool
sched_in)
{
static_call_cond(x86_pmu_sched_task)(ctx, sched_in);
+
+ /*
+ * If a new task has the RDPMC enabled, clear the dirty counters
+ * to prevent the potential leak.
+ */
+ if (sched_in && ctx && READ_ONCE(x86_pmu.attr_rdpmc) &&
+ current->mm && atomic_read(¤t->mm->context.perf_rdpmc_allowed))
+ x86_pmu_clear_dirty_counters();
}
static void x86_pmu_swap_task_ctx(struct perf_event_context *prev,
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 10c8171..55bd891 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -229,6 +229,7 @@ struct cpu_hw_events {
*/
struct perf_event *events[X86_PMC_IDX_MAX]; /* in counter order */
unsigned long active_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
+ unsigned long dirty[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
int enabled;
int n_events; /* the # of events in the below arrays */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1574b70..ef8f6f4 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -384,6 +384,7 @@ DEFINE_STATIC_KEY_FALSE(perf_sched_events);
static DECLARE_DELAYED_WORK(perf_sched_work, perf_sched_delayed);
static DEFINE_MUTEX(perf_sched_mutex);
static atomic_t perf_sched_count;
+static atomic_t perf_event_mmap_count;
static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
static DEFINE_PER_CPU(int, perf_sched_cb_usages);
@@ -3851,7 +3852,7 @@ static void perf_event_context_sched_in(struct
perf_event_context *ctx,
cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
perf_event_sched_in(cpuctx, ctx, task);
- if (cpuctx->sched_cb_usage && pmu->sched_task)
+ if (pmu->sched_task && (cpuctx->sched_cb_usage ||
atomic_read(&perf_event_mmap_count)))
pmu->sched_task(cpuctx->task_ctx, true);
perf_pmu_enable(pmu);
@@ -5988,8 +5989,10 @@ static void perf_mmap_open(struct vm_area_struct
*vma)
if (vma->vm_pgoff)
atomic_inc(&event->rb->aux_mmap_count);
- if (event->pmu->event_mapped)
+ if (event->pmu->event_mapped) {
+ atomic_inc(&perf_event_mmap_count);
event->pmu->event_mapped(event, vma->vm_mm);
+ }
}
static void perf_pmu_output_stop(struct perf_event *event);
@@ -6011,8 +6014,10 @@ static void perf_mmap_close(struct vm_area_struct
*vma)
unsigned long size = perf_data_size(rb);
bool detach_rest = false;
- if (event->pmu->event_unmapped)
+ if (event->pmu->event_unmapped) {
+ atomic_dec(&perf_event_mmap_count);
event->pmu->event_unmapped(event, vma->vm_mm);
+ }
/*
* rb->aux_mmap_count will always drop before rb->mmap_count and
@@ -6329,8 +6334,10 @@ static int perf_mmap(struct file *file, struct
vm_area_struct *vma)
vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP;
vma->vm_ops = &perf_mmap_vmops;
- if (event->pmu->event_mapped)
+ if (event->pmu->event_mapped) {
+ atomic_inc(&perf_event_mmap_count);
event->pmu->event_mapped(event, vma->vm_mm);
+ }
return ret;
}
Thanks,
Kan
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