linux-kernel - [RFC v5 11/11] powerpc/mm: Add speculative page fault

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Date:   Fri, 16 Jun 2017 19:52:35 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: [RFC v5 11/11] powerpc/mm: Add speculative page fault

This patch enable the speculative page fault on the PowerPC
architecture.

This will try a speculative page fault without holding the mmap_sem,
if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the
traditional page fault processing is done.

Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 arch/powerpc/mm/fault.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 3a7d580fdc59..4b6d0ed517ca 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -290,9 +290,31 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	if (!is_exec && user_mode(regs))
 		store_update_sp = store_updates_sp(regs);
 
-	if (user_mode(regs))
+	if (user_mode(regs)) {
 		flags |= FAULT_FLAG_USER;
 
+		/* let's try a speculative page fault without grabbing the
+		 * mmap_sem.
+		 */
+
+		/*
+		 * flags is set later based on the VMA's flags, for the common
+		 * speculative service, we need some flags to be set.
+		 */
+		if (is_write)
+			flags |= FAULT_FLAG_WRITE;
+
+		fault = handle_speculative_fault(mm, address, flags);
+		if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR))
+			goto done;
+
+		/*
+		 * Resetting flags since the following code assumes
+		 * FAULT_FLAG_WRITE is not set.
+		 */
+		flags &= ~FAULT_FLAG_WRITE;
+	}
+
 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
@@ -478,6 +500,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 			rc = 0;
 	}
 
+done:
 	/*
 	 * Major/minor page fault accounting.
 	 */
-- 
2.7.4