On 8/21/19 3:31 PM, Richard Henderson wrote:
>> Yes, that's what I mean, TARGET_PAGE_SIZE, but eventually crossing a
>> page boundary. The longer I stare at the MVCL code, the more broken it
>> is. There are more nice things buried in the PoP. MVCL does not detect
>> access exceptions beyond the next 2k. So we have to limit it there
>> differently.
> That language is indeed odd.
>
> The only reading of that paragraph that makes sense to me is that the hardware
> *must* interrupt MVCL after every 2k bytes processed. The idea that the user
> can magically write to a read-only page simply by providing length = 2MB and
> page that is initially writable is dumb. I cannot imagine that is a correct
> reading.
>
> Getting clarification from an IBM engineer on that would be good; otherwise I
> would just ignore that and proceed as if all access checks are performed.
>
FWIW, splitting the operation at every aligned 2k boundary is exactly what the
Hercules emulator does:
len3 = NOCROSS2KL(addr1,len1) ? len1 : (int)(0x800 - (addr1 & 0x7FF));
len4 = NOCROSS2KL(addr2,len2) ? len2 : (int)(0x800 - (addr2 & 0x7FF));
len = len3 < len4 ? len3 : len4;
/* Use concpy to ensure Concurrent block update consistency */
concpy (regs, dest, source, len);
After this it writes back the lengths and addresses to the
register file, and then if necessary loops back to the address
translation step.
r~
