linux-kernel - [PATCH v12 28/31] x86/mm: add speculative pagefault handling

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Date:   Tue, 16 Apr 2019 15:45:19 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     akpm@...ux-foundation.org, mhocko@...nel.org, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        aneesh.kumar@...ux.ibm.com, 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>,
        sergey.senozhatsky.work@...il.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, Daniel Jordan <daniel.m.jordan@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Ganesh Mahendran <opensource.ganesh@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Punit Agrawal <punitagrawal@...il.com>,
        vinayak menon <vinayakm.list@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        zhong jiang <zhongjiang@...wei.com>,
        Haiyan Song <haiyanx.song@...el.com>,
        Balbir Singh <bsingharora@...il.com>, sj38.park@...il.com,
        Michel Lespinasse <walken@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com,
        paulmck@...ux.vnet.ibm.com, Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: [PATCH v12 28/31] x86/mm: add speculative pagefault handling

From: Peter Zijlstra <peterz@...radead.org>

Try a speculative fault before acquiring mmap_sem, if it returns with
VM_FAULT_RETRY continue with the mmap_sem acquisition and do the
traditional fault.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

[Clearing of FAULT_FLAG_ALLOW_RETRY is now done in
 handle_speculative_fault()]
[Retry with usual fault path in the case VM_ERROR is returned by
 handle_speculative_fault(). This allows signal to be delivered]
[Don't build SPF call if !CONFIG_SPECULATIVE_PAGE_FAULT]
[Handle memory protection key fault]
Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
---
 arch/x86/mm/fault.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 667f1da36208..4390d207a7a1 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1401,6 +1401,18 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 #endif
 
+	/*
+	 * Do not try to do a speculative page fault if the fault was due to
+	 * protection keys since it can't be resolved.
+	 */
+	if (!(hw_error_code & X86_PF_PK)) {
+		fault = handle_speculative_fault(mm, address, flags);
+		if (fault != VM_FAULT_RETRY) {
+			perf_sw_event(PERF_COUNT_SW_SPF, 1, regs, address);
+			goto done;
+		}
+	}
+
 	/*
 	 * Kernel-mode access to the user address space should only occur
 	 * on well-defined single instructions listed in the exception
@@ -1499,6 +1511,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 	}
 
 	up_read(&mm->mmap_sem);
+
+done:
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		mm_fault_error(regs, hw_error_code, address, fault);
 		return;
-- 
2.21.0