Re: [PATCH] s390: PCI: fix IOMMU region init

[Christian Borntraeger]

On 26.09.19 16:34, Peter Maydell wrote:
> On Thu, 26 Sep 2019 at 15:12, Matthew Rosato <address@hidden> wrote:
>>
>> The fix in dbe9cf606c shrinks the IOMMU memory region to a size
>> that seems reasonable on the surface, however is actually too
>> small as it is based against a 0-mapped address space.  This
>> causes breakage with small guests as they can overrun the IOMMU window.
>>
>> Let's go back to the prior method of initializing iommu for now.
>>
>> Fixes: dbe9cf606c ("s390x/pci: Set the iommu region size mpcifc request")
>> Reported-by: Boris Fiuczynski <address@hidden>
>> Reported-by: Stefan Zimmerman <address@hidden>
>> Signed-off-by: Matthew Rosato <address@hidden>
> 
> So in commit f0a399dbae6a2d0e2 (Nov 2015) we used "pal - pba + 1".
> In commit f7c40aa1e7feb50bc4 (June 2016) we switched to "pal + 1".
> In commit dbe9cf606c (Jan 2019) we went back to "pal - pba + 1"
> Now we're on "pal + 1" again...
> 
> Are we really sure that this is correct and that we're not
> just going to keep looping around between these two formations
> forever? :-)

As Matt and Pierre outlined this is indeed the variant that works
reliably. I will add 
Cc: address@hidden

and apply.