Re: [Qemu-devel] [PATCH] translate-all.c: Remove writable protection feature for tb_alloc_page()

[Chen Gang]

On 2016年01月14日 18:30, Peter Maydell wrote:
> On 14 January 2016 at 10:26, Chen Gang <address@hidden> wrote:
>> On 2016年01月14日 18:05, Peter Maydell wrote:
>>> If we don't mark the page as non-writeable when we generate a TB
>>> from it, how do we detect when guest code later writes to that
>>> page (which means we need to invalidate the TB) ?
>>>
>>
>> For me, what you said above sounds reasonable, at present, that's really
>> valuable to me :-)
>>
>> I guess, you also mean: our qemu will catch the host page fault signal
>> and invalidate the TB.
> 
> Yes, this is how it works for user-mode. (For softmmu we can catch
> writes and send them via the slow path which does the check for
> whether TBs need to be invalidated; for linux-user we have no
> emulated MMU so we must rely on the host kernel sending us the
> SIGSEGV.) The bit of code that does this is at the top of
> handle_cpu_signal():
> 
>     if (is_write && h2g_valid(address)
>         && page_unprotect(h2g(address), pc, puc)) {
>         return 1;
>     }
> 

OK, thank you very much!  :-)


Thanks.
-- 
Chen Gang (陈刚)

Open, share, and attitude like air, water, and life which God blessed