Re: [PATCH v5 04/19] accel/tcg: Adjust probe_access call to page_check_range

[Richard Henderson]

On 5/8/20 9:13 AM, Peter Maydell wrote:
> On Fri, 8 May 2020 at 16:44, Richard Henderson
> <address@hidden> wrote:
>>
>> We have validated that addr+size does not cross a page boundary.
>> Therefore we need to validate exactly one page.  We can achieve
>> that passing any value 1 <= x <= size to page_check_range.
>>
>> Passing 1 will simplify the next patch.
> 
> It's not clear to me how it simplifies the next patch, though --
> we have the size right there in the new function which
> calls page_check_range(), don't we? So I still don't
> understand why we're using '1' -- it isn't allowing
> us to avoid passing the size into probe_access_internal(),
> because we need to pass it anyway.
> 
> We've gone round this multiple times now so I feel like
> I must be missing something here.

While probe_access() has a size parameter, probe_access_flags() does not.

For probe_access_internal(), I currently have a "fault_size" parameter that
gets passed to tlb_fill, which is "size" for probe_access() and 0 for
probe_access_flags().

I *could* add another "check_size" parameter to probe_access_internal, to be
passed on to page_check_range(). It would be "size" for probe_access() and 1
for probe_access_flags().  But what's the point?  Always passing 1 to
page_check_range() has the same effect.

I feel like I'm missing something with your objection.


r~