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

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Date:	Mon, 27 Apr 2009 07:35:16 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Andi Kleen <ak@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer

>-----Original Message-----
>From: Andi Kleen [mailto:ak@...ux.intel.com]
>Sent: Saturday, April 25, 2009 8:41 AM
>To: Metzger, Markus T; Linux Kernel Mailing List
>Subject: Re: [rfc 2/2] x86, bts: use physically non-contiguous trace buffer
>
>Markus Metzger wrote:
>> 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.
>
>For test purposes you could hack vmalloc.c to allocate more pages
>and only put in every second/third/... into the mapping. You would
>just need to add another to loop to __vmalloc_area_node() that allocates
>more. That should give you non continuous mappings unless you're really unlucky.

Thanks.

I got enough feedback that the existing method is preferable to using vmalloc
that I dropped it again.

regards,
markus.


>
>-Andi
>
>
>>
>>
>> Reported-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>> CC: Andrew Morton <akpm@...ux-foundation.org>
>> Signed-off-by: Markus Metzger <markus.t.metzger@...el.com>
>> ---
>>  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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