Re: [qemu-s390x] [Qemu-devel] [PATCH v2 04/28] s390x/tcg: MVCL: Process max 2k bytes at a time

[David Hildenbrand]

On 11.09.19 17:07, Richard Henderson wrote:
> On 9/11/19 10:52 AM, Richard Henderson wrote:
>> The code within Hercules breaks the action at every 2k address boundary -- 
>> for
>> both src and dest.  That's the only way that actually makes sense to me, as
>> otherwise we end up allowing userspace to read/write into a page without
>> permission.  Which is a security hole.
> 
> Also, doesn't "2k" come from the old esa/360 page size?

I have no idea, I was very confused with that.

> 
> Which means that we could break at 4k pages instead of 2k now
> and the program wouldn't really be able to tell the difference.

What I had in a previous iteration was to simply process until the end
of the page(s), to not cross pages (there is one special case with 2k
vs. 4k when crossing pages when wrapping and running into a
low-address-protection). So essentially what you suggest. I can add that.

-- 

Thanks,

David / dhildenb