[Xen-devel] [RFC PATCHv2 0/7]: x86/xen: fixes for mapping high MMIO regions

[David Vrabel <david.vrabel@xxxxxxxxxx>]

This a likely fix for the problems with mapping high MMIO regions in
certain cases (e.g., the RDMA drivers) as not all mappers were
specifing _PAGE_IOMAP which meant no valid MFN could be found and the
resulting PTEs would be set as not present, causing subsequent faults.

It assumes that anything that isn't RAM (whether ballooned out or not)
is an I/O region and thus should be 1:1 in the p2m.  Specifically, the
region after the end of the E820 map and the region beyond the end of
the p2m.  Ballooned frames are still marked as missing in the p2m as
before.

As a follow on, pte_mfn_to_pfn() and pte_pfn_to_mfn() are modified to
not use the _PAGE_IOMAP PTE flag and MFN to PFN and PFN to MFN
translations will now do the right thing for all I/O regions.  This
means the Xen-specific _PAGE_IOMAP can be removed,

This series is posted as an RFC since it hasn't see a level of testing
I required (in particular it's not tested with a device with a high
MMIO region).  This is definetly 3.15 material since anything to do
with the p2m has a high risk.

You may find it useful to apply patch #3 to more easily review the
updated p2m diagram.

Changes in v2:
- fix to actually set end-of-RAM to 512 GiB region as 1:1.
- introduce p2m_mid_identity to efficiently store large 1:1 regions.
- Split the _PAGE_IOMAP patch into Xen and generic x86 halves.

David


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel