Re: [Xen-devel] [PATCH v2 11/19] xen/arm32: Use alternative to skip the check of pending serrors

[Wei Chen <Wei.Chen@xxxxxxx>]

On 2017/3/31 5:29, Stefano Stabellini wrote:
> On Thu, 30 Mar 2017, Julien Grall wrote:
>> Hi Wei,
>>
>> On 30/03/17 10:13, Wei Chen wrote:
>>> We have provided an option to administrator to determine how to
>>> handle the SErrors. In order to skip the check of pending SError,
>>> in conventional way, we have to read the option every time before
>>> we try to check the pending SError. This will add overhead to check
>>> the option at every trap.
>>>
>>> The ARM32 supports the alternative patching feature. We can use an
>>> ALTERNATIVE to avoid checking option at every trap. We added a new
>>> cpufeature named "SKIP_CHECK_PENDING_VSERROR". This feature will be
>>> enabled when the option is not diverse.
>>>
>>> Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
>>
>> Reviewed-by: Julien Grall <julien.grall@xxxxxxx>
>>
>>> ---
>>
>> Stefano, this is requiring the alternative patch (see [1]) which is still in
>> review.
>>
>> Wei, a general rule is to mention the dependencies between series. So we 
>> don't
>> apply by mistake in the wrong order.
>
> Right. Thanks Wei for sending both the other patch and this series
> together, that helps me avoiding mistakes.
>
> But please add a note about the dependencies, just in case I forget.
>

Stefano and Julien, thank you. I would place a note about the
dependencies in next version.

>
>> Cheers,
>>
>> [1] 
>> https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg04132.html
>>
>>>  xen/arch/arm/arm32/entry.S | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
>>> index 2187226..105cae8 100644
>>> --- a/xen/arch/arm/arm32/entry.S
>>> +++ b/xen/arch/arm/arm32/entry.S
>>> @@ -1,5 +1,6 @@
>>>  #include <asm/asm_defns.h>
>>>  #include <asm/regs.h>
>>> +#include <asm/alternative.h>
>>>  #include <public/xen.h>
>>>
>>>  #define SAVE_ONE_BANKED(reg)    mrs r11, reg; str r11, [sp, #UREGS_##reg]
>>> @@ -44,6 +45,14 @@ save_guest_regs:
>>>          SAVE_BANKED(fiq)
>>>          SAVE_ONE_BANKED(R8_fiq); SAVE_ONE_BANKED(R9_fiq);
>>> SAVE_ONE_BANKED(R10_fiq)
>>>          SAVE_ONE_BANKED(R11_fiq); SAVE_ONE_BANKED(R12_fiq);
>>> +
>>> +        /*
>>> +         * If the SKIP_CHECK_PENDING_VSERROR has been set in the cpu
>>> feature,
>>> +         * the checking of pending SErrors will be skipped.
>>> +         */
>>> +        ALTERNATIVE("nop",
>>> +                    "b skip_check",
>>> +                    SKIP_CHECK_PENDING_VSERROR)
>>>          /*
>>>           * Start to check pending virtual abort in the gap of Guest -> HYP
>>>           * world switch.
>>> @@ -99,6 +108,7 @@ abort_guest_exit_end:
>>>           */
>>>          bne return_from_trap
>>>
>>> +skip_check:
>>>          mov pc, lr
>>>
>>>  #define DEFINE_TRAP_ENTRY(trap)                                         \
>>>
>>
>> --
>> Julien Grall
>>
>


-- 
Regards,
Wei Chen

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