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Yongji Xie 0a701aa637 PCI: Add pcibios_default_alignment() for arch-specific alignment control
When VFIO passes through a PCI device to a guest, it does not allow the
guest to mmap BARs that are smaller than PAGE_SIZE unless it can reserve
the rest of the page (see vfio_pci_probe_mmaps()). This is because a page
might contain several small BARs for unrelated devices and a guest should
not be able to access all of them.

VFIO emulates guest accesses to non-mappable BARs, which is functional but
slow. On systems with large page sizes, e.g., PowerNV with 64K pages, BARs
are more likely to share a page and performance is more likely to be a
problem.

Add a weak function to set default alignment for all PCI devices.  An arch
can override it to force the PCI core to place memory BARs on their own
pages.

Signed-off-by: Yongji Xie <elohimes@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
2017-04-19 12:51:25 -05:00
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drivers PCI: Add pcibios_default_alignment() for arch-specific alignment control 2017-04-19 12:51:25 -05:00
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include PCI: Make PCI_ROM_ADDRESS_MASK a 32-bit constant 2017-04-18 14:46:57 -05:00
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Linux kernel
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