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vfio/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, 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>
This commit is contained in:
Jason Cai (Xiang Feng) 2018-03-22 12:52:16 +08:00 committed by Alex Williamson
parent c9f89c3f87
commit 356e88ebe4
1 changed files with 15 additions and 10 deletions
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25
drivers/vfio/vfio_iommu_type1.c
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@ -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;
}