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Re: [Xen-devel] [PATCHv4 0/8] x86/xen: fixes for mapping high MMIO regions (and remove _PAGE_IOMAP)

On Mon, Feb 03, 2014 at 05:01:29PM +0000, David Vrabel wrote:
> [ x86 maintainers, this is predominately a Xen series but the end
> result is the _PAGE_IOMAP PTE flag is removed. See patch #8. ]
> This a 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 has been tested (in dom0) on all unique machines we have
> in out test lab (~100 machines), some of which have PCI devices with
> BARs above the end of RAM.

This looks good to me and thank you for taking a stab at it.

In the coming weeks I can run some more tests with this patchset where:
 - it is used in a PV PCI domU.
 - it is used in a PV PCI domU with backend devices (so say a NIC
   is exported to it and said NIC is backend for other PV devices).
 - it is used on a regular PV and we do ballooning, migration ,etc.
 - Get cycles on the box that has InfiniBand MMIOs in the 60TB range.
> Note this does not fix a 32-bit dom0 trying to access BARs above 16 TB
> as this is a caused by MFNs/PFNs being limited to 32-bits (unsigned
> long).
> You may find it useful to apply patch #3 to more easily review the
> updated p2m diagram.
> Changes in v4:
> - fix p2m_mid_identity initialization.
> Changes in v3 (not posted):
> - use correct end of e820
> - fix xen_remap_domain_mfn_range()
> 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

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