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Subject[RFC v2] vfio iommu type1: improve memory pinning process for raw PFN mapping
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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. Thus, it can
significantly improve VM's boot up time when passing through devices
via VFIO.

Signed-off-by: Jason Cai (Xiang Feng) <jason.cai@linux.alibaba.com>
---
drivers/vfio/vfio_iommu_type1.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index e30e29ae4819..82ccfa350315 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -385,7 +385,6 @@ 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 */
@@ -396,14 +395,22 @@ 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(npage, (long)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__,
@@ -423,13 +430,12 @@ 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);
@@ -447,10 +453,8 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,

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;
}
--
2.13.6
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