[PATCH 6/6] kvm/book3s: drop mmap_sem now that locked_vm is atomic

[Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>]

With locked_vm now an atomic, there is no need to take mmap_sem as
writer.  Delete and refactor accordingly.

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Alexey Kardashevskiy <aik@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: <linux-mm@xxxxxxxxx>
Cc: <kvm-ppc@xxxxxxxxxxxxxxx>
Cc: <linuxppc-dev@xxxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
---
 arch/powerpc/kvm/book3s_64_vio.c | 34 +++++++++++---------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index e7fdb6d10eeb..8e034c3a5d25 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -56,7 +56,7 @@ static unsigned long kvmppc_stt_pages(unsigned long tce_pages)
 	return tce_pages + ALIGN(stt_bytes, PAGE_SIZE) / PAGE_SIZE;
 }
 
-static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
+static long kvmppc_account_memlimit(unsigned long pages, bool inc)
 {
 	long ret = 0;
 	s64 locked_vm;
@@ -64,33 +64,23 @@ static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
 	if (!current || !current->mm)
 		return ret; /* process exited */
 
-	down_write(&current->mm->mmap_sem);
-
-	locked_vm = atomic64_read(&current->mm->locked_vm);
 	if (inc) {
-		unsigned long locked, lock_limit;
+		unsigned long lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
-		locked = locked_vm + stt_pages;
-		lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+		locked_vm = atomic64_add_return(pages, &current->mm->locked_vm);
+		if (locked_vm > lock_limit && !capable(CAP_IPC_LOCK)) {
 			ret = -ENOMEM;
-		else
-			atomic64_add(stt_pages, &current->mm->locked_vm);
+			atomic64_sub(pages, &current->mm->locked_vm);
+		}
 	} else {
-		if (WARN_ON_ONCE(stt_pages > locked_vm))
-			stt_pages = locked_vm;
-
-		atomic64_sub(stt_pages, &current->mm->locked_vm);
+		locked_vm = atomic64_sub_return(pages, &current->mm->locked_vm);
+		WARN_ON_ONCE(locked_vm < 0);
 	}
 
-	pr_debug("[%d] RLIMIT_MEMLOCK KVM %c%ld %ld/%ld%s\n", current->pid,
-			inc ? '+' : '-',
-			stt_pages << PAGE_SHIFT,
-			atomic64_read(&current->mm->locked_vm) << PAGE_SHIFT,
-			rlimit(RLIMIT_MEMLOCK),
-			ret ? " - exceeded" : "");
-
-	up_write(&current->mm->mmap_sem);
+	pr_debug("[%d] RLIMIT_MEMLOCK KVM %c%lu %lld/%lu%s\n", current->pid,
+			inc ? '+' : '-', pages << PAGE_SHIFT,
+			locked_vm << PAGE_SHIFT,
+			rlimit(RLIMIT_MEMLOCK), ret ? " - exceeded" : "");
 
 	return ret;
 }
-- 
2.21.0