[rfc 2/2] x86, bts: use physically non-contiguous trace buffer

[Markus Metzger]

Use vmalloc to allocate the branch trace buffer.

Peter Zijlstra suggested to use vmalloc rather than kmalloc to
allocate the potentially multi-page branch trace buffer.

Is there a way to have vmalloc allocate a physically non-contiguous
buffer for test purposes? Ideally, the memory area would have big
holes in it with sensitive data in between so I would know immediately
when this is overwritten.


Reported-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
---
 arch/x86/kernel/ptrace.c |    5 	3 +	2 -	0 !
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: b/arch/x86/kernel/ptrace.c
===================================================================
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -22,6 +22,7 @@
 #include <linux/seccomp.h>
 #include <linux/signal.h>
 #include <linux/workqueue.h>
+#include <linux/vmalloc.h>
 
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
@@ -626,7 +627,7 @@ static int alloc_bts_buffer(struct bts_c
 	if (err < 0)
 		return err;
 
-	buffer = kzalloc(size, GFP_KERNEL);
+	buffer = vmalloc(size);
 	if (!buffer)
 		goto out_refund;
 
@@ -646,7 +647,7 @@ static inline void free_bts_buffer(struc
 	if (!context->buffer)
 		return;
 
-	kfree(context->buffer);
+	vfree(context->buffer);
 	context->buffer = NULL;
 
 	refund_locked_memory(context->mm, context->size);
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