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

[Daniel Jordan]

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.jor...@oracle.com>
Cc: Alexey Kardashevskiy <a...@ozlabs.ru>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Christoph Lameter <c...@linux.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Paul Mackerras <pau...@ozlabs.org>
Cc: <linux...@kvack.org>
Cc: <kvm-...@vger.kernel.org>
Cc: <linuxppc-dev@lists.ozlabs.org>
Cc: <linux-ker...@vger.kernel.org>
---
 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