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Subject[PATCH v12 28/31] x86/mm: add speculative pagefault handling
Date
From: Peter Zijlstra <peterz@infradead.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@infradead.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@linux.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
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