[PATCH] powerpc-powernv: align BARs to PAGE_SIZE on powernv platform

[Alexey Kardashevskiy]

VFIO adds a separate memory region for every BAR and tries
to mmap() it to provide direct BAR mapping to the guest.
If it succeedes, QEMU registers this address with kvm_set_phys_mem().
However it is not always possible because such a BAR should
be host page size aligned. In this case VFIO uses "slow" path
and emulated BAR access in QEMU.

In order to avoid "slow" path, BARs have to be PAGE_SIZE aligned
in the host kernel and this is what the patch does.

The patch adds powernv platform specific hook which makes all
BARs sizes 64K aligned. The pci_reassigndev_resource_alignment()
function from drivers/pci/pci.c has been used as a reference.

This is purely an optimization patch, the things will work without
it, just a bit slower.

Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
---
 arch/powerpc/platforms/powernv/setup.c |   26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index db1ad1c..331838e 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -25,6 +25,7 @@
 #include <linux/of.h>
 #include <linux/interrupt.h>
 #include <linux/bug.h>
+#include <linux/pci.h>
 
 #include <asm/machdep.h>
 #include <asm/firmware.h>
@@ -179,6 +180,30 @@ static int __init pnv_probe(void)
 	return 1;
 }
 
+static void pnv_pcibios_fixup_resources(struct pci_dev *pdev)
+{
+	struct resource *r;
+	int i;
+
+	/*
+	 * Aligning resources to PAGE_SIZE in order to
+	 * support "fast" path for PCI BAR access under VFIO
+	 * which maps every BAR individually to the guest
+	 * so BARs have to be PAGE aligned.
+	 */
+	for (i = 0; i <= PCI_ROM_RESOURCE; i++) {
+		r = &pdev->resource[i];
+		if (!r->flags)
+			continue;
+		pr_debug("powernv: %s, aligning BAR#%d %llx..%llx",
+			pdev->dev.kobj.name, i, r->start, r->end);
+		r->end = PAGE_ALIGN(r->end - r->start + 1) - 1;
+		r->start = 0;
+		r->flags |= IORESOURCE_UNSET;
+		pr_debug(" to  %llx..%llx\n", r->start, r->end);
+	}
+}
+
 define_machine(powernv) {
 	.name			= "PowerNV",
 	.probe			= pnv_probe,
@@ -189,6 +214,7 @@ define_machine(powernv) {
 	.progress		= pnv_progress,
 	.power_save             = power7_idle,
 	.calibrate_decr		= generic_calibrate_decr,
+	.pcibios_fixup_resources= pnv_pcibios_fixup_resources,
 #ifdef CONFIG_KEXEC
 	.kexec_cpu_down		= pnv_kexec_cpu_down,
 #endif
-- 
1.7.10.4