[U-Boot] [PATCH v2 2/2] arm: Set TTB XN bit in case DCACHE_OFF for LPAE mode

Keerthy
2016-10-30T01:59:03Z

On Saturday 29 October 2016 11:19 PM, Marek Vasut wrote:
> On 10/29/2016 07:47 PM, Tom Rini wrote:
>> On Sat, Oct 29, 2016 at 07:44:34PM +0200, Marek Vasut wrote:
>>> On 10/29/2016 07:41 PM, Tom Rini wrote:
>>>> On Sat, Oct 29, 2016 at 03:19:10PM +0530, Keerthy wrote:
>>>>
>>>>> While we setup the mmu initially we mark set_section_dcache with
>>>>> DCACHE_OFF flag. In case of non-LPAE mode the DCACHE_OFF macro
>>>>> is rightly defined with TTB_SECT_XN_MASK set so as to mark all the
>>>>> 4GB XN. In case of LPAE mode XN(Execute-never) bit is not set with
>>>>> DCACHE_OFF. Hence XN bit is not set by default for DCACHE_OFF which
>>>>> keeps all the regions execute okay and this leads to random speculative
>>>>> fetches in random memory regions which was eventually caught by kernel
>>>>> omap-l3-noc driver.
>>>>>
>>>>> Fix this to mark the regions as XN by default.
>>>>>
>>>>> Signed-off-by: Keerthy <j-keerthy@ti.com>
>>>>> Reviewed-by: Alexander Graf <agraf@suse.de>
>>>>
>>>> Reviewed-by: Tom Rini <trini@konsulko.com>
>>>>
>>> Isn't this patch exactly undoing the following one ?
>>>
>>> commit 8890c2fbe6ed4c5ca9a61f21e846a55f8f2c38fc
>>> Author: Marek Vasut <>
>>> Date: Tue Dec 29 19:44:02 2015 +0100
>>>
>>> arm: Remove S bit from MMU section entry
>>>
>>> Restore the old behavior of the MMU section entries configuration,
>>> which is without the S-bit.
>>
>> Is it? I guess perhaps you and Keerthy need to chat then as there's
>> some other problem they're addressing.
>
> Ummmm, wait a second, I think this one adds XN bit and the previous one
> removed S bit. I think I was wrong, but please double-check this. I
> recall we had some odd cache issues on V7 back then.

Marek,

First and foremost if we git blame on the file:
arch/arm/include/asm/system.h

your commit:
8890c2fbe6ed4c5ca9a61f21e846a55f8f2c38fc

arm: Remove S bit from MMU section entry

It is removing S bit under
#elif defined(CONFIG_CPU_V7)

I am adding the missing XN bit under:
#ifdef CONFIG_ARMV7_LPAE

So we are dealing with different modes.

In a nutshell your patch removes S bit from MMU section entry for
non-LPAE cases for ARMV7 and mine adds XN bit for LPAE cases.

Hope this clears out the confusion.

- Keerthy

>