[PATCH v4 14/16] vfio: powerpc/spapr: Reuse locked_vm accounting helpers

[Alexey Kardashevskiy <aik@ozlabs.ru>]

There are helpers to account locked pages in locked_vm counter, this
reuses these helpers in VFIO-SPAPR-IOMMU driver.

While we are here, update the comment explaining why RLIMIT_MEMLOCK
might be required to be bigger than entire guest RAM.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v4:
* added comment explaining how big the ulimit should be
* used try_increment_locked_vm/decrement_locked_vm
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index d9845af..6ed0fc3 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -58,7 +58,6 @@ static void tce_iommu_take_ownership_notify(struct spapr_tce_iommu_group *data,
 static int tce_iommu_enable(struct tce_container *container)
 {
 	int ret = 0;
-	unsigned long locked, lock_limit, npages;
 	struct iommu_table *tbl;
 	struct spapr_tce_iommu_group *data;
 
@@ -92,24 +91,24 @@ static int tce_iommu_enable(struct tce_container *container)
 	 * Also we don't have a nice way to fail on H_PUT_TCE due to ulimits,
 	 * that would effectively kill the guest at random points, much better
 	 * enforcing the limit based on the max that the guest can map.
+	 *
+	 * Unfortunately at the moment it counts whole tables, no matter how
+	 * much memory the guest has. I.e. for 4GB guest and 4 IOMMU groups
+	 * each with 2GB DMA window, 8GB will be counted here. The reason for
+	 * this is that we cannot tell here the amount of RAM used by the guest
+	 * as this information is only available from KVM and VFIO is
+	 * KVM agnostic.
 	 */
 	tbl = data->ops->get_table(data, TCE_DEFAULT_WINDOW);
 	if (!tbl)
 		return -ENXIO;
 
-	down_write(&current->mm->mmap_sem);
-	npages = (tbl->it_size << IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
-	locked = current->mm->locked_vm + npages;
-	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-	if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
-		pr_warn("RLIMIT_MEMLOCK (%ld) exceeded\n",
-				rlimit(RLIMIT_MEMLOCK));
-		ret = -ENOMEM;
-	} else {
-		current->mm->locked_vm += npages;
-		container->enabled = true;
-	}
-	up_write(&current->mm->mmap_sem);
+	ret = try_increment_locked_vm((tbl->it_size << IOMMU_PAGE_SHIFT_4K) >>
+			PAGE_SHIFT);
+	if (ret)
+		return ret;
+
+	container->enabled = true;
 
 	return ret;
 }
@@ -135,10 +134,8 @@ static void tce_iommu_disable(struct tce_container *container)
 	if (!tbl)
 		return;
 
-	down_write(&current->mm->mmap_sem);
-	current->mm->locked_vm -= (tbl->it_size <<
-			IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
-	up_write(&current->mm->mmap_sem);
+	decrement_locked_vm((tbl->it_size << IOMMU_PAGE_SHIFT_4K) >>
+			PAGE_SHIFT);
 }
 
 static void *tce_iommu_open(unsigned long arg)
-- 
2.0.0