linux-kernel - [PATCH v5 3/3] vfio/type1: Reduce repetitive calls in vfio_pin_pages

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Date:   Mon, 17 Apr 2017 16:38:10 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     alex.williamson@...hat.com, kvm@...r.kernel.org
Cc:     eric.auger@...hat.com, kwankhede@...dia.com, peterx@...hat.com,
        linux-kernel@...r.kernel.org, slp@...hat.com
Subject: [PATCH v5 3/3] vfio/type1: Reduce repetitive calls in
 vfio_pin_pages_remote()

vfio_pin_pages_remote() is typically called to iterate over a range
of memory.  Testing CAP_IPC_LOCK is relatively expensive, so it makes
sense to push it up to the caller, which can then repeatedly call
vfio_pin_pages_remote() using that value.  This can show nearly a 20%
improvement on the worst case path through VFIO_IOMMU_MAP_DMA with
contiguous page mapping disabled.  Testing RLIMIT_MEMLOCK is much more
lightweight, but we bring it along on the same principle and it does
seem to show a marginal improvement.

Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---
 drivers/vfio/vfio_iommu_type1.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 372e4f626138..8549cb111627 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -380,10 +380,10 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
  * first page and all consecutive pages with the same locking.
  */
 static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
-				  long npage, unsigned long *pfn_base)
+				  long npage, unsigned long *pfn_base,
+				  bool lock_cap, unsigned long limit)
 {
-	unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-	bool lock_cap = capable(CAP_IPC_LOCK);
+	unsigned long pfn = 0;
 	long ret, pinned = 0, lock_acct = 0;
 	bool rsvd;
 	dma_addr_t iova = vaddr - dma->vaddr + dma->iova;
@@ -924,13 +924,15 @@ static int vfio_pin_map_dma(struct vfio_iommu *iommu, struct vfio_dma *dma,
 	unsigned long vaddr = dma->vaddr;
 	size_t size = map_size;
 	long npage;
-	unsigned long pfn;
+	unsigned long pfn, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	bool lock_cap = capable(CAP_IPC_LOCK);
 	int ret = 0;
 
 	while (size) {
 		/* Pin a contiguous chunk of memory */
 		npage = vfio_pin_pages_remote(dma, vaddr + dma->size,
-					      size >> PAGE_SHIFT, &pfn);
+					      size >> PAGE_SHIFT, &pfn,
+					      lock_cap, limit);
 		if (npage <= 0) {
 			WARN_ON(!npage);
 			ret = (int)npage;
@@ -1040,6 +1042,8 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 {
 	struct vfio_domain *d;
 	struct rb_node *n;
+	unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	bool lock_cap = capable(CAP_IPC_LOCK);
 	int ret;
 
 	/* Arbitrarily pick the first domain in the list for lookups */
@@ -1086,7 +1090,8 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 
 				npage = vfio_pin_pages_remote(dma, vaddr,
 							      n >> PAGE_SHIFT,
-							      &pfn);
+							      &pfn, lock_cap,
+							      limit);
 				if (npage <= 0) {
 					WARN_ON(!npage);
 					ret = (int)npage;