[PATCH 8/8] powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <dja at axtens.net>

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

Signed-off-by: Daniel Axtens <dja at axtens.net>
Signed-off-by: Christopher M. Riedl <cmr at codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 3b97e3681a8f..0f4ff7a5bfc1 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -779,18 +779,22 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	 */
 	regs->msr &= ~MSR_TS_MASK;
 
-	if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
+	if (!user_read_access_begin(uc, sizeof(*uc)))
 		goto badframe;
+
+	unsafe_get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR], badframe_block);
+
 	if (MSR_TM_ACTIVE(msr)) {
 		/* We recheckpoint on return. */
 		struct ucontext __user *uc_transact;
 
 		/* Trying to start TM on non TM system */
 		if (!cpu_has_feature(CPU_FTR_TM))
-			goto badframe;
+			goto badframe_block;
+
+		unsafe_get_user(uc_transact, &uc->uc_link, badframe_block);
+		user_read_access_end();
 
-		if (__get_user(uc_transact, &uc->uc_link))
-			goto badframe;
 		if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
 					   &uc_transact->uc_mcontext))
 			goto badframe;
@@ -810,12 +814,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		 * causing a TM bad thing.
 		 */
 		current->thread.regs->msr &= ~MSR_TS_MASK;
+
+#ifndef CONFIG_PPC_TRANSACTIONAL_MEM
 		if (!user_read_access_begin(uc, sizeof(*uc)))
-			return -EFAULT;
-		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
-			user_read_access_end();
 			goto badframe;
-		}
+#endif
+		unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext,
+					  badframe_block);
 		user_read_access_end();
 	}
 
@@ -825,6 +830,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
 
+badframe_block:
+	user_read_access_end();
 badframe:
 	signal_fault(current, regs, "rt_sigreturn", uc);
 
-- 
2.28.0