[PATCH] efi-entry.S: add dsb and isb

[Tom Lendacky]

On 11/12/2014 12:09 PM, Mark Rutland wrote:
> Hi Tom,
>
> On Wed, Nov 12, 2014 at 05:50:39PM +0000, Tom Lendacky wrote:
>> On 11/12/2014 10:58 AM, Mark Rutland wrote:
>>> Hi Joel,
>>>
>>> I've Cc'd a few people who were involved in authoring this.
>>>
>>> I have an alternative patch [1] that also adds some missing maintenance.
>>> Would you be able to give that a go?
>>
>> I applied the referenced patch and have booted about two dozen times
>> without seeing a synchronous exception.  Prior to either patch I would
>> see a synchronous exception about every three or four (re)boots.
>
> Thank you for testing.
>
> May I add your Tested-by?

Hi Mark,

Certainly.

Tested-by: Tom Lendacky <thomas.lendacky at amd.com>

Thanks,
Tom

>
> Cheers,
> Mark.
>
>> Thanks,
>> Tom
>>
>>>
>>> On Tue, Nov 11, 2014 at 06:32:04AM +0000, Joel Schopp wrote:
>>>> Add a dsb and isb after the instruction flush before the data cache and
>>>> mm offing.  Without this patch I am seeing synchronous exceptions occur
>>>> every few boots.
>>>>
>>>> Signed-off-by: Joel Schopp <joel.schopp at amd.com>
>>>> Tested-by: Tom Lendacky <Thomas.Lendacky at amd.com>
>>>> ---
>>>>    arch/arm64/kernel/efi-entry.S |    6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
>>>> index 619b1dd..7d95eda 100644
>>>> --- a/arch/arm64/kernel/efi-entry.S
>>>> +++ b/arch/arm64/kernel/efi-entry.S
>>>> @@ -76,6 +76,12 @@ ENTRY(efi_stub_entry)
>>>>    	bl	__flush_dcache_area
>>>>    	ic	ialluis
>>>>
>>>> +	/* We need to sync again after the instruction cache sync
>>>> +	 * and before turning off the dcache and mmu
>>>> +	 */
>>>> +	dsb	sy
>>>> +	isb
>>>
>>> In my series I reasoned that it wasn't necessary to have an ISB before
>>> we disabled the MMU. The current image must already be visible to the
>>> I-cache, so the I-cache can't have stale entries for it. We don't
>>> disable the MMU until after the image is visible at the PoC, so we
>>> shouldn't break the visbility of the current image to the I-cache.
>>>
>>> There is a bug in that We don't flush the current image in case of
>>> relocation, but I don't see how the ISB would help there.
>>>
>>> Thanks,
>>> Mark.
>>>
>>>> +
>>>>    	/* Turn off Dcache and MMU */
>>>>    	mrs	x0, CurrentEL
>>>>    	cmp	x0, #CurrentEL_EL2
>>>>
>>>>
>>>> _______________________________________________
>>>> linux-arm-kernel mailing list
>>>> linux-arm-kernel at lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>>>
>>>
>>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/301779.html
>>>
>>