linux-kernel - [PATCH] ARM: Fix userspace enter on LPAE with CC_OPTIMIZE_FOR

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Message-Id: <200d273a83906a68a1c4a9298c415980737be811.1715781469.git.geert+renesas@glider.be>
Date: Wed, 15 May 2024 16:02:14 +0200
From: Geert Uytterhoeven <geert+renesas@...der.be>
To: Russell King <linux@...linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Kees Cook <keescook@...omium.org>,
	Russell King <rmk+kernel@...linux.org.uk>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Stefan Wahren <wahrenst@....net>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-renesas-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] ARM: Fix userspace enter on LPAE with CC_OPTIMIZE_FOR_SIZE=y

Booting an LPAE-enabled kernel built with CONFIG_CC_OPTIMIZE_FOR_SIZE=y
fails when starting userspace:

    Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
    CPU: 1 PID: 1 Comm: init Tainted: G        W        N 6.9.0-rc1-koelsch-00004-g7af5b901e847 #1930
    Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
    Call trace:
     unwind_backtrace from show_stack+0x10/0x14
     show_stack from dump_stack_lvl+0x78/0xa8
     dump_stack_lvl from panic+0x118/0x398
     panic from do_exit+0x1ec/0x938
     do_exit from sys_exit_group+0x0/0x10
    ---[ end Kernel panic - not syncing: Attempted to kill init!  exitcode=0x00000004 ]---

Add the missing memory clobber to cpu_set_ttbcr(), as suggested by
Russell King.

Force inlining of uaccess_save_and_enable(), as suggested by Ard
Biesheuvel.

The latter fixes booting on Koelsch.

Fixes: 7af5b901e84743c6 ("ARM: 9358/2: Implement PAN for LPAE by TTBR0 page table walks disablement")
Closes: https://lore.kernel.org/r/CAMuHMdWTAJcZ9BReWNhpmsgkOzQxLNb5OhNYxzxv6D5TSh2fwQ@mail.gmail.com/
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
Feel free to fold into the original commit.

Apparently the "From: Catalin Marinas <catalin.marinas@....com>" in
https://lore.kernel.org/r/20240312-arm32-lpae-pan-v3-4-532647afcd38@linaro.org
is not reflected in commit 7af5b901e84743c6?
---
 arch/arm/include/asm/proc-fns.h | 2 +-
 arch/arm/include/asm/uaccess.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/proc-fns.h b/arch/arm/include/asm/proc-fns.h
index 9b3105a2a5e0691e..b4986a23d8528a50 100644
--- a/arch/arm/include/asm/proc-fns.h
+++ b/arch/arm/include/asm/proc-fns.h
@@ -187,7 +187,7 @@ static inline unsigned int cpu_get_ttbcr(void)
 
 static inline void cpu_set_ttbcr(unsigned int ttbcr)
 {
-	asm("mcr p15, 0, %0, c2, c0, 2" : : "r" (ttbcr));
+	asm volatile("mcr p15, 0, %0, c2, c0, 2" : : "r" (ttbcr) : "memory");
 }
 
 #else	/*!CONFIG_MMU */
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 25d21d7d6e3efee0..6c9c16d767cfd5df 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -47,7 +47,7 @@ static __always_inline void uaccess_restore(unsigned int flags)
 
 #elif defined(CONFIG_CPU_TTBR0_PAN)
 
-static inline unsigned int uaccess_save_and_enable(void)
+static __always_inline unsigned int uaccess_save_and_enable(void)
 {
 	unsigned int old_ttbcr = cpu_get_ttbcr();
 
-- 
2.34.1