From da929f6af4689c75868dc373b4549f53945b5af0 Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Wed, 19 Apr 2017 14:56:30 +0200 Subject: [PATCH] powerpc/mm: Evaluate user_mode(regs) only once in do_page_fault() Analysis of the assembly code shows that when using user_mode(regs), at least the 'andi.' is redone all the time, and also the 'lwz ,132(r31)' most of the time. With the new form, the 'is_user' is mapped to cr4, then all further use of is_user results in just things like 'beq cr4,218 ' Without the patch: 50: 81 1e 00 84 lwz r8,132(r30) 54: 71 09 40 00 andi. r9,r8,16384 58: 40 82 00 0c bne 64 84: 81 3e 00 84 lwz r9,132(r30) 8c: 71 2a 40 00 andi. r10,r9,16384 90: 41 a2 01 64 beq 1f4 d4: 81 3e 00 84 lwz r9,132(r30) dc: 71 28 40 00 andi. r8,r9,16384 e0: 41 82 02 08 beq 2e8 108: 81 3e 00 84 lwz r9,132(r30) 110: 71 28 40 00 andi. r8,r9,16384 118: 41 82 02 28 beq 340 1e4: 81 3e 00 84 lwz r9,132(r30) 1e8: 71 2a 40 00 andi. r10,r9,16384 1ec: 40 82 01 68 bne 354 228: 81 3e 00 84 lwz r9,132(r30) 22c: 71 28 40 00 andi. r8,r9,16384 230: 41 82 ff c4 beq 1f4 288: 71 2a 40 00 andi. r10,r9,16384 294: 41 a2 fe 60 beq f4 50c: 81 3e 00 84 lwz r9,132(r30) 514: 71 2a 40 00 andi. r10,r9,16384 518: 40 a2 fc e0 bne 1f8 534: 81 3e 00 84 lwz r9,132(r30) 53c: 71 2a 40 00 andi. r10,r9,16384 540: 41 82 fc b8 beq 1f8 This patch creates a local var called 'is_user' which contains the result of user_mode(regs) With the patch: 20: 81 03 00 84 lwz r8,132(r3) 48: 55 09 97 fe rlwinm r9,r8,18,31,31 58: 2e 09 00 00 cmpwi cr4,r9,0 5c: 40 92 00 0c bne cr4,68 88: 41 b2 01 90 beq cr4,218 d4: 40 92 01 d0 bne cr4,2a4 120: 41 b2 00 f8 beq cr4,218 138: 41 b2 ff a0 beq cr4,d8 1d4: 40 92 00 e0 bne cr4,2b4 Signed-off-by: Christophe Leroy Reviewed-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- arch/powerpc/mm/fault.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 059e762e8995..ab9622120696 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -206,6 +206,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, int is_write = 0; int trap = TRAP(regs); int is_exec = trap == 0x400; + int is_user = user_mode(regs); int fault; int rc = 0, store_update_sp = 0; @@ -247,7 +248,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * The kernel should never take an execute fault nor should it * take a page fault to a kernel address. */ - if (!user_mode(regs) && (is_exec || (address >= TASK_SIZE))) { + if (!is_user && (is_exec || (address >= TASK_SIZE))) { rc = SIGSEGV; goto bail; } @@ -266,7 +267,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, local_irq_enable(); if (faulthandler_disabled() || mm == NULL) { - if (!user_mode(regs)) { + if (!is_user) { rc = SIGSEGV; goto bail; } @@ -287,10 +288,10 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (is_write && user_mode(regs)) + if (is_write && is_user) store_update_sp = store_updates_sp(regs); - if (user_mode(regs)) + if (is_user) flags |= FAULT_FLAG_USER; /* When running in the kernel we expect faults to occur only to @@ -309,7 +310,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * thus avoiding the deadlock. */ if (!down_read_trylock(&mm->mmap_sem)) { - if (!user_mode(regs) && !search_exception_tables(regs->nip)) + if (!is_user && !search_exception_tables(regs->nip)) goto bad_area_nosemaphore; retry: @@ -509,7 +510,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, bad_area_nosemaphore: /* User mode accesses cause a SIGSEGV */ - if (user_mode(regs)) { + if (is_user) { _exception(SIGSEGV, regs, code, address); goto bail; } -- GitLab