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Commit 0a701aa6 authored by Yongji Xie's avatar Yongji Xie Committed by Bjorn Helgaas
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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: default avatarYongji Xie <elohimes@gmail.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
parent c9c75143

drivers/pci/pci.c

+8 −2
Original line number Diff line number Diff line
@@ -4947,6 +4947,11 @@ void pci_ignore_hotplug(struct pci_dev *dev) 
}

EXPORT_SYMBOL_GPL(pci_ignore_hotplug);



resource_size_t __weak pcibios_default_alignment(void)

{

	return 0;

}



#define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE

static char resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0};

static DEFINE_SPINLOCK(resource_alignment_lock);
@@ -4962,14 +4967,15 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev) 
{

	int seg, bus, slot, func, align_order, count;

	unsigned short vendor, device, subsystem_vendor, subsystem_device;

	resource_size_t align = 0;

	resource_size_t align = pcibios_default_alignment();

	char *p;



	spin_lock(&resource_alignment_lock);

	p = resource_alignment_param;

	if (!*p)

	if (!*p && !align)

		goto out;

	if (pci_has_flag(PCI_PROBE_ONLY)) {

		align = 0;

		pr_info_once("PCI: Ignoring requested alignments (PCI_PROBE_ONLY)\n");

		goto out;

	}