x86, ds: allow small debug store buffers

Check the buffer size more precisely to allow buffers for exactly
one element provided the base address is already properly aligned.

Add a debug store selftest.

Reported-by: Stephane Eranian <eranian@googlemail.com>
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Cc: roland@redhat.com
Cc: eranian@googlemail.com
Cc: oleg@redhat.com
Cc: juan.villacis@intel.com
Cc: ak@linux.jf.intel.com
LKML-Reference: <20090403144606.139137000@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/ds.c b/arch/x86/kernel/ds.c
index ebfb0fd..4e05157 100644 (file)
--- a/arch/x86/kernel/ds.c
+++ b/arch/x86/kernel/ds.c
@@ -656,6 +656,7 @@ static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
 {
        struct ds_context *context;
        int error;
+       size_t req_size;
 
        error = -EOPNOTSUPP;
        if (!ds_cfg.sizeof_rec[qual])
@@ -665,9 +666,13 @@ static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
        if (!base)
                goto out;
 
-       /* We need space for alignment adjustments in ds_init_ds_trace(). */
+       req_size = ds_cfg.sizeof_rec[qual];
+       /* We might need space for alignment adjustments. */
+       if (!IS_ALIGNED((unsigned long)base, DS_ALIGNMENT))
+               req_size += DS_ALIGNMENT;
+
        error = -EINVAL;
-       if (size < (DS_ALIGNMENT + ds_cfg.sizeof_rec[qual]))
+       if (size < req_size)
                goto out;
 
        if (th != (size_t)-1) {

diff --git a/arch/x86/kernel/ds_selftest.c b/arch/x86/kernel/ds_selftest.c
index a40b253..5f104a0 100644 (file)
--- a/arch/x86/kernel/ds_selftest.c
+++ b/arch/x86/kernel/ds_selftest.c
@@ -16,8 +16,8 @@
 #include <asm/ds.h>
 
 
-#define BUFFER_SIZE    521 /* Intentionally chose an odd size. */
-
+#define BUFFER_SIZE            521     /* Intentionally chose an odd size. */
+#define SMALL_BUFFER_SIZE      24      /* A single bts entry. */
 
 struct ds_selftest_bts_conf {
        struct bts_tracer *tracer;
@@ -381,7 +381,7 @@ int ds_selftest_bts(void)
        conf.suspend = ds_suspend_bts_noirq;
        conf.resume = ds_resume_bts_noirq;
        conf.tracer =
-               ds_request_bts_task(current, buffer, BUFFER_SIZE,
+               ds_request_bts_task(current, buffer, SMALL_BUFFER_SIZE,
                                   NULL, (size_t)-1, BTS_KERNEL);
        local_irq_save(irq);
        ds_selftest_bts_cpu(&conf);