Re: [Qemu-devel] [v3 PATCH] target-mips: implement UserLocal Register

[James Hogan]

On 29/05/14 14:08, Aurelien Jarno wrote:
> On Thu, May 29, 2014 at 01:01:38PM +0000, Petar Jovanovic wrote:
>>> While adding MIPS_HFLAG_HWRENA_ULR is a good idea for performance
>>> reasons, I don't think we should add MIPS_HFLAG_CP0UL. This value is
>>> always the same (true or false) during all the run time of the
>>> qemu-system-mips binary, and thus we don't need to take care of code
>>> generated with it being true or being false.
>>
>> Initial version of this patch did not have this flag, but it was added
>> as requested in code review.
>> What do you suggest?
> 
> Well maybe I missed something, but it looks to me the value can never
> change as CP0_Config3 is a read-only register. If I am right, probably
> the best is to check directly env->CP0_Config3.
> 

loadvm/migration will write Config3, possibly with a different value if
the snapshot being loaded is an older one without userlocal support.
Does tlb_flush() definitely get called in that case? I can't see how
from a quick look, although memory will have been reloaded so perhaps
that is sufficient to guarantee no old translations are lying around.

By the way v3 looks reasonable to me, and seems to work (although I
failed to test savevm/loadvm as it seemed to be already broken with the
particular guest kernel I was using).

Cheers
James