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

[Peter Maydell]

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? :-)

thanks
-- PMM