linux-kernel - [PATCH v3 20/20] powerpc/mm: Add speculative page fault

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Message-Id: <1504894024-2750-21-git-send-email-ldufour@linux.vnet.ibm.com>
Date:   Fri,  8 Sep 2017 20:07:04 +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>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
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>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: [PATCH v3 20/20] 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 VM_FAULT_RETRY, the mmap_sem is acquired and the
traditional page fault processing is done.

Support is only provide for BOOK3S_64 currently because:
- require CONFIG_PPC_STD_MMU because checks done in
  set_access_flags_filter()
- require BOOK3S because we can't support for book3e_hugetlb_preload()
  called by update_mmu_cache()

Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h |  5 +++++
 arch/powerpc/mm/fault.c                      | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index b9aff515b4de..470203daf97e 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -314,6 +314,11 @@ extern unsigned long pci_io_base;
 /* Advertise support for _PAGE_SPECIAL */
 #define __HAVE_ARCH_PTE_SPECIAL
 
+/* Advertise that we call the Speculative Page Fault handler */
+#if defined(CONFIG_PPC_BOOK3S_64)
+#define __HAVE_ARCH_CALL_SPF
+#endif
+
 #ifndef __ASSEMBLY__
 
 /*
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 4797d08581ce..97c7de242627 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -442,6 +442,20 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 	if (is_exec)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+#if defined(__HAVE_ARCH_CALL_SPF)
+	if (is_user) {
+		/* let's try a speculative page fault without grabbing the
+		 * mmap_sem.
+		 */
+		fault = handle_speculative_fault(mm, address, flags);
+		if (!(fault & VM_FAULT_RETRY)) {
+			perf_sw_event(PERF_COUNT_SW_SPF, 1,
+				      regs, address);
+			goto done;
+		}
+	}
+#endif /* defined(__HAVE_ARCH_CALL_SPF) */
+
 	/* 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
@@ -526,6 +540,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	up_read(&current->mm->mmap_sem);
 
+done:
 	if (unlikely(fault & VM_FAULT_ERROR))
 		return mm_fault_error(regs, address, fault);
 
-- 
2.7.4