[PATCH v3 8/8] powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <d...@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 <d...@axtens.net>
Co-developed-by: Christopher M. Riedl <c...@codefail.de>
Signed-off-by: Christopher M. Riedl <c...@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 7e62d62ef482..1b1e39663999 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -784,8 +784,11 @@ SYSCALL_DEFINE0(rt_sigreturn)
        regs->msr &= ~MSR_TS_MASK;
 #endif
 
-       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)) {
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
                /* We recheckpoint on return. */
@@ -793,10 +796,12 @@ SYSCALL_DEFINE0(rt_sigreturn)
 
                /* 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;
@@ -815,12 +820,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
                 * causing a TM bad thing.
                 */
                current->thread.regs->msr &= ~MSR_TS_MASK;
-               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;
-               }
+               unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext,
+                                         badframe_block);
+
                user_read_access_end();
        }
 
@@ -830,6 +832,8 @@ 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);
 
-- 
2.26.1