vfio/type1: Improve memory pinning process for raw PFN mapping

When using vfio to pass through a PCIe device (e.g. a GPU card) that
has a huge BAR (e.g. 16GB), a lot of cycles are wasted on memory
pinning because PFNs of PCI BAR are not backed by struct page, and
the corresponding VMA has flag VM_PFNMAP.

With this change, when pinning a region which is a raw PFN mapping,
it can skip unnecessary user memory pinning process, and thus, can
significantly improve VM's boot up time when passing through devices
via VFIO. In my test on a Xeon E5 2.6GHz, the time mapping a 16GB
BAR was reduced from about 0.4s to 1.5us.

Signed-off-by: Jason Cai (Xiang Feng) <jason.cai@linux.alibaba.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 3c082451ab1a..5c212bf29640 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -404,7 +404,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 {
         unsigned long pfn = 0;
         long ret, pinned = 0, lock_acct = 0;
-        bool rsvd;
         dma_addr_t iova = vaddr - dma->vaddr + dma->iova;
 
         /* This code path is only user initiated */
@@ -415,14 +414,23 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
         if (ret)
                 return ret;
 
+        if (is_invalid_reserved_pfn(*pfn_base)) {
+                struct vm_area_struct *vma;
+
+                down_read(&current->mm->mmap_sem);
+                vma = find_vma_intersection(current->mm, vaddr, vaddr + 1);
+                pinned = min_t(long, npage, vma_pages(vma));
+                up_read(&current->mm->mmap_sem);
+                return pinned;
+        }
+
         pinned++;
-        rsvd = is_invalid_reserved_pfn(*pfn_base);
 
         /*
          * Reserved pages aren't counted against the user, externally pinned
          * pages are already counted against the user.
          */
-        if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+        if (!vfio_find_vpfn(dma, iova)) {
                 if (!lock_cap && current->mm->locked_vm + 1 > limit) {
                         put_pfn(*pfn_base, dma->prot);
                         pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", __func__,
@@ -442,13 +450,12 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
                 if (ret)
                         break;
 
-                if (pfn != *pfn_base + pinned ||
-                    rsvd != is_invalid_reserved_pfn(pfn)) {
+                if (pfn != *pfn_base + pinned) {
                         put_pfn(pfn, dma->prot);
                         break;
                 }
 
-                if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+                if (!vfio_find_vpfn(dma, iova)) {
                         if (!lock_cap &&
                             current->mm->locked_vm + lock_acct + 1 > limit) {
                                 put_pfn(pfn, dma->prot);
@@ -466,10 +473,8 @@ out:
 
 unpin_out:
         if (ret) {
-                if (!rsvd) {
-                        for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
-                                put_pfn(pfn, dma->prot);
-                }
+                for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
+                        put_pfn(pfn, dma->prot);
 
                 return ret;
         }