linux-kernel - [PATCH] powerpc/signal32: Force inlining of __unsafe_save_user_regs() and save_tm_user_regs

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Date:   Mon,  5 Jun 2023 10:58:35 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/signal32: Force inlining of __unsafe_save_user_regs() and save_tm_user_regs_unsafe()

Looking at generated code for handle_signal32() shows calls to a
function called __unsafe_save_user_regs.constprop.0 while user access
is open.

And that __unsafe_save_user_regs.constprop.0 function has two nops at
the begining, allowing it to be traced, which is unexpected during
user access open window.

The solution could be to mark __unsafe_save_user_regs() no trace, but
to be on the safe side the most efficient is to flag it __always_inline
as already done for function __unsafe_restore_general_regs(). The
function is relatively small and only called twice, so the size
increase will remain in the noise.

Do the same with save_tm_user_regs_unsafe() as it may suffer the
same issue.

Fixes: ef75e7318294 ("powerpc/signal32: Transform save_user_regs() and save_tm_user_regs() in 'unsafe' version")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/signal_32.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index c114c7f25645..7a718ed32b27 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -264,8 +264,9 @@ static void prepare_save_user_regs(int ctx_has_vsx_region)
 #endif
 }
 
-static int __unsafe_save_user_regs(struct pt_regs *regs, struct mcontext __user *frame,
-				   struct mcontext __user *tm_frame, int ctx_has_vsx_region)
+static __always_inline int
+__unsafe_save_user_regs(struct pt_regs *regs, struct mcontext __user *frame,
+			struct mcontext __user *tm_frame, int ctx_has_vsx_region)
 {
 	unsigned long msr = regs->msr;
 
@@ -364,8 +365,9 @@ static void prepare_save_tm_user_regs(void)
 		current->thread.ckvrsave = mfspr(SPRN_VRSAVE);
 }
 
-static int save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *frame,
-				    struct mcontext __user *tm_frame, unsigned long msr)
+static __always_inline int
+save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *frame,
+			 struct mcontext __user *tm_frame, unsigned long msr)
 {
 	/* Save both sets of general registers */
 	unsafe_save_general_regs(&current->thread.ckpt_regs, frame, failed);
@@ -444,8 +446,9 @@ static int save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user
 #else
 static void prepare_save_tm_user_regs(void) { }
 
-static int save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *frame,
-				    struct mcontext __user *tm_frame, unsigned long msr)
+static __always_inline int
+save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *frame,
+			 struct mcontext __user *tm_frame, unsigned long msr)
 {
 	return 0;
 }
-- 
2.40.1