vfio-pci supports huge_fault for PCI MMIO BARs and will insert pud and
pmd mappings for well aligned mappings. follow_pfnmap_start() walks the
page table and therefore knows the page mask of the level where the
address is found and returns this through follow_pfnmap_args.pgmask.
Subsequent pfns from this address until the end of the mapping page are
necessarily consecutive. Use this information to retrieve a range of
pfnmap pfns in a single pass.
With optimal mappings and alignment on systems with 1GB pud and 4KB
page size, this reduces iterations for DMA mapping PCI BARs by a
factor of 256K. In real world testing, the overhead of iterating
pfns for a VM DMA mapping a 32GB PCI BAR is reduced from ~1s to
sub-millisecond overhead.
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
drivers/vfio/vfio_iommu_type1.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 939920454da7..6f3e8d981311 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -520,7 +520,7 @@ static void vfio_batch_fini(struct vfio_batch *batch)
static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
unsigned long vaddr, unsigned long *pfn,
- bool write_fault)
+ unsigned long *pgmask, bool write_fault)
{
struct follow_pfnmap_args args = { .vma = vma, .address = vaddr };
int ret;
@@ -544,10 +544,12 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
return ret;
}
- if (write_fault && !args.writable)
+ if (write_fault && !args.writable) {
ret = -EFAULT;
- else
+ } else {
*pfn = args.pfn;
+ *pgmask = args.pgmask;
+ }
follow_pfnmap_end(&args);
return ret;
@@ -590,15 +592,23 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
vma = vma_lookup(mm, vaddr);
if (vma && vma->vm_flags & VM_PFNMAP) {
- ret = follow_fault_pfn(vma, mm, vaddr, pfn, prot & IOMMU_WRITE);
+ unsigned long pgmask;
+
+ ret = follow_fault_pfn(vma, mm, vaddr, pfn, &pgmask,
+ prot & IOMMU_WRITE);
if (ret == -EAGAIN)
goto retry;
if (!ret) {
- if (is_invalid_reserved_pfn(*pfn))
- ret = 1;
- else
+ if (is_invalid_reserved_pfn(*pfn)) {
+ unsigned long epfn;
+
+ epfn = (((*pfn << PAGE_SHIFT) + ~pgmask + 1)
+ & pgmask) >> PAGE_SHIFT;
+ ret = min_t(int, npages, epfn - *pfn);
+ } else {
ret = -EFAULT;
+ }
}
}
done:
--
2.47.1
