Re: [PATCH 0/2] Update use_goto_tb() in hppa and rx targets

[Richard Henderson]

On 5/19/20 11:38 AM, Alex Bennée wrote:
> 
> Richard Henderson <address@hidden> writes:
> 
>> On 5/19/20 9:21 AM, Ahmed Karaman wrote:
>>> The issue arose because the page crossings check in use_goto_tb()
>>> function is required only in the system mode. Checking it in both modes
>>> causes an unnecessary overhead in the user mode.
>>
>> It is not only required in system mode.
>>
>> You can see failures in user-mode if you modify executable pages, or change
>> their permissions with mmap.  Such as if the guest program contains a
>> JIT.
> 
> If we kept better track couldn't we just tb_flush() if a new +x region
> gets mmaped? I guess that would be sub-optimal compared to having a
> translation cache per mmap region.
> 

Yes, this could definitely be improved.  Noticing changes to PROT_EXEC via
mprotect, for one.


r~