x86, smap: Reduce the SMAP overhead for signal handling

Signal handling contains a bunch of accesses to individual user space
items, which causes an excessive number of STAC and CLAC
instructions.  Instead, let get/put_user_try ... get/put_user_catch()
contain the STAC and CLAC instructions.

This means that get/put_user_try no longer nests, and furthermore that
it is no longer legal to use user space access functions other than
__get/put_user_ex() inside those blocks.  However, these macros are
x86-specific anyway and are only used in the signal-handling paths; a
simple reordering of moving the larger subroutine calls out of the
try...catch blocks resolves that problem.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-12-git-send-email-hpa@linux.intel.com

1 files changed, 7 insertions, 5 deletions

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 673ac9b63d6b..05e62a312bd9 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -250,11 +250,12 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
 
                 get_user_ex(tmp, &sc->fpstate);
                 buf = compat_ptr(tmp);
-                err |= restore_i387_xstate_ia32(buf);
 
                 get_user_ex(*pax, &sc->ax);
         } get_user_catch(err);
 
+        err |= restore_i387_xstate_ia32(buf);
+
         return err;
 }
 
@@ -502,7 +503,6 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(sig, &frame->sig);
                 put_user_ex(ptr_to_compat(&frame->info), &frame->pinfo);
                 put_user_ex(ptr_to_compat(&frame->uc), &frame->puc);
-                err |= copy_siginfo_to_user32(&frame->info, info);
 
                 /* Create the ucontext.  */
                 if (cpu_has_xsave)
@@ -514,9 +514,6 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(sas_ss_flags(regs->sp),
                             &frame->uc.uc_stack.ss_flags);
                 put_user_ex(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
-                err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
-                                             regs, set->sig[0]);
-                err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
                 if (ka->sa.sa_flags & SA_RESTORER)
                         restorer = ka->sa.sa_restorer;
@@ -532,6 +529,11 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 put_user_ex(*((u64 *)&code), (u64 *)frame->retcode);
         } put_user_catch(err);
 
+        err |= copy_siginfo_to_user32(&frame->info, info);
+        err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
+                                     regs, set->sig[0]);
+        err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
+
         if (err)
                 return -EFAULT;