Re: [EXTERNAL] [PATCH 1/2] target/ppc: Fix slbia TLB invalidation gap

[Nicholas Piggin]

Cédric Le Goater's on March 19, 2020 2:45 am:
> On 3/18/20 5:41 AM, Nicholas Piggin wrote:
>> slbia must invalidate TLBs even if it does not remove a valid SLB
>> entry, because slbmte can overwrite valid entries without removing
>> their TLBs.
>> 
>> As the architecture says, slbia invalidates all lookaside information,
>> not conditionally based on if it removed valid entries.
>> 
>> It does not seem possible for POWER8 or earlier Linux kernels to hit
>> this bug because it never changes its kernel SLB translations, and it
>> should always have valid entries if any accesses are made to usespace
>> regions. However other operating systems which may modify SLB entry 0
>> or do more fancy things with segments might be affected.
> 
> Did you hit the bug on the other OS ? 

No, hit it when fixing POWER9 hash.

>  
>> When POWER9 slbia support is added in the next patch, this becomes a
>> real problem because some new slbia variants don't invalidate all
>> non-zero entries.
>> 
>> Signed-off-by: Nicholas Piggin <address@hidden>
> 
> Looks correct.
> 
> Reviewed-by: Cédric Le Goater <address@hidden>

Thanks,
Nick