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* [PATCH] vfio iommu type1: improve memory pinning process for raw PFN mapping
@ 2018-03-19  2:30 Jason Cai (Xiang Feng)
  2018-03-20 21:33 ` Alex Williamson
  0 siblings, 1 reply; 5+ messages in thread
From: Jason Cai (Xiang Feng) @ 2018-03-19  2:30 UTC (permalink / raw)
  To: Alex Williamson, pbonzini, kvm, linux-kernel, linux-mm
  Cc: gnehzuil, Jason Cai (Xiang Feng)

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>
---
 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 45657e2b1ff7..0658f35318b8 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -397,7 +397,6 @@ 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 */
@@ -408,14 +407,22 @@ 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__,
@@ -435,13 +442,12 @@ 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);
@@ -459,10 +465,8 @@ 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

^ permalink raw reply	[flat|nested] 5+ messages in thread
* [PATCH] vfio iommu type1: improve memory pinning process for raw PFN mapping
@ 2018-03-22  4:52 Jason Cai (Xiang Feng)
  2018-03-22 21:48 ` Alex Williamson
  0 siblings, 1 reply; 5+ messages in thread
From: Jason Cai (Xiang Feng) @ 2018-03-22  4:52 UTC (permalink / raw)
  To: alex.williamson, pbonzini, kvm, linux-kernel, linux-mm
  Cc: gnehzuil, jason.cai

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>
---
 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 45657e2b1ff7..0658f35318b8 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -397,7 +397,6 @@ 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 */
@@ -408,14 +407,22 @@ 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__,
@@ -435,13 +442,12 @@ 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);
@@ -459,10 +465,8 @@ 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

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2018-03-22 21:48 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-03-19  2:30 [PATCH] vfio iommu type1: improve memory pinning process for raw PFN mapping Jason Cai (Xiang Feng)
2018-03-20 21:33 ` Alex Williamson
2018-03-20 22:04   ` Alex Williamson
2018-03-22  4:52 Jason Cai (Xiang Feng)
2018-03-22 21:48 ` Alex Williamson

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