Hello,
Starting with 4.15 I noticed that BTS is sporadically missing the tail
of the trace in the perf_event data buffer. It shows as
[decode error (1): instruction overflow]
in GDB. Chances to see this are higher the longer the debuggee is
running. With this [1] tiny patch to one of GDB's tests, I am able to
reproduce it reliably on my box. To run the test, use:
$ make -s check RUNTESTFLAGS="gdb.btrace/exception.exp"
from the gdb/ sub-directory in the GDB build directory.
The issue remains when I use 'nopti' on the kernel command-line.
Bisecting yielded commit
c1961a4 x86/events/intel/ds: Map debug buffers in cpu_entry_area
I reverted the commit on top of v4.17 [2] and the issue disappears
when I use 'nopti' on the kernel command-line.
regards,
markus.
[1]
diff --git a/gdb/testsuite/gdb.btrace/exception.exp
b/gdb/testsuite/gdb.btrace/exception.exp
index 9408d61..a24ddd3 100755
--- a/gdb/testsuite/gdb.btrace/exception.exp
+++ b/gdb/testsuite/gdb.btrace/exception.exp
@@ -36,16 +36,12 @@ if ![runto_main] {
gdb_test_no_output "set record function-call-history-size 0"
# set bp
-set bp_1 [gdb_get_line_number "bp.1" $srcfile]
set bp_2 [gdb_get_line_number "bp.2" $srcfile]
-gdb_breakpoint $bp_1
gdb_breakpoint $bp_2
-# trace the code between the two breakpoints
-gdb_continue_to_breakpoint "cont to bp.1" ".*$srcfile:$bp_1\r\n.*"
# increase the BTS buffer size - the trace can be quite big
-gdb_test_no_output "set record btrace bts buffer-size 128000"
-gdb_test_no_output "record btrace"
+gdb_test_no_output "set record btrace bts buffer-size 1024000"
+gdb_test_no_output "record btrace bts"
gdb_continue_to_breakpoint "cont to bp.2" ".*$srcfile:$bp_2\r\n.*"
# show the flat branch trace
[2]
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 8a10a045b57b..46381f73c595 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -3,7 +3,6 @@
#include <linux/types.h>
#include <linux/slab.h>
-#include <asm/cpu_entry_area.h>
#include <asm/perf_event.h>
#include <asm/tlbflush.h>
#include <asm/insn.h>
@@ -282,67 +281,17 @@ void fini_debug_store_on_cpu(int cpu)
static DEFINE_PER_CPU(void *, insn_buffer);
-static void ds_update_cea(void *cea, void *addr, size_t size, pgprot_t prot)
-{
- unsigned long start = (unsigned long)cea;
- phys_addr_t pa;
- size_t msz = 0;
-
- pa = virt_to_phys(addr);
-
- preempt_disable();
- for (; msz < size; msz += PAGE_SIZE, pa += PAGE_SIZE, cea += PAGE_SIZE)
- cea_set_pte(cea, pa, prot);
-
- /*
- * This is a cross-CPU update of the cpu_entry_area, we must shoot down
- * all TLB entries for it.
- */
- flush_tlb_kernel_range(start, start + size);
- preempt_enable();
-}
-
-static void ds_clear_cea(void *cea, size_t size)
-{
- unsigned long start = (unsigned long)cea;
- size_t msz = 0;
-
- preempt_disable();
- for (; msz < size; msz += PAGE_SIZE, cea += PAGE_SIZE)
- cea_set_pte(cea, 0, PAGE_NONE);
-
- flush_tlb_kernel_range(start, start + size);
- preempt_enable();
-}
-
-static void *dsalloc_pages(size_t size, gfp_t flags, int cpu)
-{
- unsigned int order = get_order(size);
- int node = cpu_to_node(cpu);
- struct page *page;
-
- page = __alloc_pages_node(node, flags | __GFP_ZERO, order);
- return page ? page_address(page) : NULL;
-}
-
-static void dsfree_pages(const void *buffer, size_t size)
-{
- if (buffer)
- free_pages((unsigned long)buffer, get_order(size));
-}
-
static int alloc_pebs_buffer(int cpu)
{
- struct cpu_hw_events *hwev = per_cpu_ptr(&cpu_hw_events, cpu);
- struct debug_store *ds = hwev->ds;
- size_t bsiz = x86_pmu.pebs_buffer_size;
- int max, node = cpu_to_node(cpu);
- void *buffer, *ibuffer, *cea;
+ struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
+ int node = cpu_to_node(cpu);
+ int max;
+ void *buffer, *ibuffer;
if (!x86_pmu.pebs)
return 0;
- buffer = dsalloc_pages(bsiz, GFP_KERNEL, cpu);
+ buffer = kzalloc_node(x86_pmu.pebs_buffer_size, GFP_KERNEL, node);
if (unlikely(!buffer))
return -ENOMEM;
@@ -353,94 +302,99 @@ static int alloc_pebs_buffer(int cpu)
if (x86_pmu.intel_cap.pebs_format < 2) {
ibuffer = kzalloc_node(PEBS_FIXUP_SIZE, GFP_KERNEL, node);
if (!ibuffer) {
- dsfree_pages(buffer, bsiz);
+ kfree(buffer);
return -ENOMEM;
}
per_cpu(insn_buffer, cpu) = ibuffer;
}
- hwev->ds_pebs_vaddr = buffer;
- /* Update the cpu entry area mapping */
- cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers.pebs_buffer;
- ds->pebs_buffer_base = (unsigned long) cea;
- ds_update_cea(cea, buffer, bsiz, PAGE_KERNEL);
+
+ max = x86_pmu.pebs_buffer_size / x86_pmu.pebs_record_size;
+
+ ds->pebs_buffer_base = (u64)(unsigned long)buffer;
ds->pebs_index = ds->pebs_buffer_base;
- max = x86_pmu.pebs_record_size * (bsiz / x86_pmu.pebs_record_size);
- ds->pebs_absolute_maximum = ds->pebs_buffer_base + max;
+ ds->pebs_absolute_maximum = ds->pebs_buffer_base +
+ max * x86_pmu.pebs_record_size;
+
return 0;
}
static void release_pebs_buffer(int cpu)
{
- struct cpu_hw_events *hwev = per_cpu_ptr(&cpu_hw_events, cpu);
- void *cea;
+ struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
- if (!x86_pmu.pebs)
+ if (!ds || !x86_pmu.pebs)
return;
kfree(per_cpu(insn_buffer, cpu));
per_cpu(insn_buffer, cpu) = NULL;
- /* Clear the fixmap */
- cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers.pebs_buffer;
- ds_clear_cea(cea, x86_pmu.pebs_buffer_size);
- dsfree_pages(hwev->ds_pebs_vaddr, x86_pmu.pebs_buffer_size);
- hwev->ds_pebs_vaddr = NULL;
+ kfree((void *)(unsigned long)ds->pebs_buffer_base);
+ ds->pebs_buffer_base = 0;
}
static int alloc_bts_buffer(int cpu)
{
- struct cpu_hw_events *hwev = per_cpu_ptr(&cpu_hw_events, cpu);
- struct debug_store *ds = hwev->ds;
- void *buffer, *cea;
- int max;
+ struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
+ int node = cpu_to_node(cpu);
+ int max, thresh;
+ void *buffer;
if (!x86_pmu.bts)
return 0;
- buffer = dsalloc_pages(BTS_BUFFER_SIZE, GFP_KERNEL | __GFP_NOWARN, cpu);
+ buffer = kzalloc_node(BTS_BUFFER_SIZE, GFP_KERNEL | __GFP_NOWARN, node);
if (unlikely(!buffer)) {
WARN_ONCE(1, "%s: BTS buffer allocation failure\n", __func__);
return -ENOMEM;
}
- hwev->ds_bts_vaddr = buffer;
- /* Update the fixmap */
- cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers.bts_buffer;
- ds->bts_buffer_base = (unsigned long) cea;
- ds_update_cea(cea, buffer, BTS_BUFFER_SIZE, PAGE_KERNEL);
+
+ max = BTS_BUFFER_SIZE / BTS_RECORD_SIZE;
+ thresh = max / 16;
+
+ ds->bts_buffer_base = (u64)(unsigned long)buffer;
ds->bts_index = ds->bts_buffer_base;
- max = BTS_RECORD_SIZE * (BTS_BUFFER_SIZE / BTS_RECORD_SIZE);
- ds->bts_absolute_maximum = ds->bts_buffer_base + max;
- ds->bts_interrupt_threshold = ds->bts_absolute_maximum - (max / 16);
+ ds->bts_absolute_maximum = ds->bts_buffer_base +
+ max * BTS_RECORD_SIZE;
+ ds->bts_interrupt_threshold = ds->bts_absolute_maximum -
+ thresh * BTS_RECORD_SIZE;
+
return 0;
}
static void release_bts_buffer(int cpu)
{
- struct cpu_hw_events *hwev = per_cpu_ptr(&cpu_hw_events, cpu);
- void *cea;
+ struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
- if (!x86_pmu.bts)
+ if (!ds || !x86_pmu.bts)
return;
- /* Clear the fixmap */
- cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers.bts_buffer;
- ds_clear_cea(cea, BTS_BUFFER_SIZE);
- dsfree_pages(hwev->ds_bts_vaddr, BTS_BUFFER_SIZE);
- hwev->ds_bts_vaddr = NULL;
+ kfree((void *)(unsigned long)ds->bts_buffer_base);
+ ds->bts_buffer_base = 0;
}
static int alloc_ds_buffer(int cpu)
{
- struct debug_store *ds = &get_cpu_entry_area(cpu)->cpu_debug_store;
+ int node = cpu_to_node(cpu);
+ struct debug_store *ds;
+
+ ds = kzalloc_node(sizeof(*ds), GFP_KERNEL, node);
+ if (unlikely(!ds))
+ return -ENOMEM;
- memset(ds, 0, sizeof(*ds));
per_cpu(cpu_hw_events, cpu).ds = ds;
+
return 0;
}
static void release_ds_buffer(int cpu)
{
+ struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
+
+ if (!ds)
+ return;
+
per_cpu(cpu_hw_events, cpu).ds = NULL;
+ kfree(ds);
}
void release_ds_buffers(void)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 9f3711470ec1..4eb9c12915e4 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -200,8 +200,6 @@ struct cpu_hw_events {
* Intel DebugStore bits
*/
struct debug_store *ds;
- void *ds_pebs_vaddr;
- void *ds_bts_vaddr;
u64 pebs_enabled;
int n_pebs;
int n_large_pebs;
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