, Thomas Bogendoerfer [off-list ref], linux-parisc@vger.kernel.org, Max Filippov [off-list ref], linux-kernel@vger.kernel.org, Johannes Berg [off-list ref], Dinh Nguyen [off-list ref], linux-riscv@lists.infradead.org, Palmer Dabbelt [off-list ref], Sven Schnelle [off-list ref], linux-alpha@vger.kernel.org, Ivan Kokshaysky [off-list ref], Andrew Morton [off-list ref], linuxppc-dev@lists.ozlabs.org, "David S . Miller" [off-list ref]

Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev" [off-list ref]

On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:

On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:

quoted

Am 29.05.22 um 22:33 schrieb Heiko Carstens:
[...]

quoted

Guess the patch below on top of your patch is what we want.
Just for clarification: if gmap is not NULL then the process is a kvm
process. So, depending on the workload, this optimization makes sense.

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 4608cc962ecf..e1d40ca341b7 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c

@@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
  	/* The fault is fully completed (including releasing mmap lock) */
  	if (fault & VM_FAULT_COMPLETED) {
-		/*
-		 * Gmap will need the mmap lock again, so retake it.  TODO:
-		 * only conditionally take the lock when CONFIG_PGSTE set.
-		 */
-		mmap_read_lock(mm);
-		goto out_gmap;
+		if (gmap) {
+			mmap_read_lock(mm);
+			goto out_gmap;
+		}
+		goto out;

Hmm, right after I replied I found "goto out" could be problematic, since
all s390 callers of do_exception() will assume it an error condition (side
note: "goto out_gmap" contains one step to clear "fault" to 0).  I'll
replace this with "return 0" instead if it looks good to both of you.

I'll wait for a confirmation before reposting.  Thanks,

-- 
Peter Xu