From 3855ab614df4818c833864572559a97fd9f9a299 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Sat, 18 Sep 2021 10:44:36 +0200 Subject: [PATCH] ARM: smp: Free up the TLS register while running in the kernel To prepare for a subsequent patch that stores the current task pointer in the user space TLS register while running in the kernel, modify the set_tls and switch_tls routines not to touch the register directly, and update the return to user space code to load the correct value. Signed-off-by: Ard Biesheuvel Reviewed-by: Linus Walleij Tested-by: Amit Daniel Kachhap --- arch/arm/include/asm/tls.h | 10 +++++++--- arch/arm/kernel/entry-header.S | 8 ++++++++ 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h index 5a66c3b..c329649 100644 --- a/arch/arm/include/asm/tls.h +++ b/arch/arm/include/asm/tls.h @@ -12,8 +12,8 @@ .macro switch_tls_v6k, base, tp, tpuser, tmp1, tmp2 mrc p15, 0, \tmp2, c13, c0, 2 @ get the user r/w register - mcr p15, 0, \tp, c13, c0, 3 @ set TLS register - mcr p15, 0, \tpuser, c13, c0, 2 @ and the user r/w register + @ TLS register update is deferred until return to user space + mcr p15, 0, \tpuser, c13, c0, 2 @ set the user r/w register str \tmp2, [\base, #TI_TP_VALUE + 4] @ save it .endm @@ -38,18 +38,22 @@ #ifdef CONFIG_TLS_REG_EMUL #define tls_emu 1 #define has_tls_reg 1 +#define defer_tls_reg_update 0 #define switch_tls switch_tls_none #elif defined(CONFIG_CPU_V6) #define tls_emu 0 #define has_tls_reg (elf_hwcap & HWCAP_TLS) +#define defer_tls_reg_update 0 #define switch_tls switch_tls_v6 #elif defined(CONFIG_CPU_32v6K) #define tls_emu 0 #define has_tls_reg 1 +#define defer_tls_reg_update 1 #define switch_tls switch_tls_v6k #else #define tls_emu 0 #define has_tls_reg 0 +#define defer_tls_reg_update 0 #define switch_tls switch_tls_software #endif @@ -77,7 +81,7 @@ static inline void set_tls(unsigned long val) */ barrier(); - if (!tls_emu) { + if (!tls_emu && !defer_tls_reg_update) { if (has_tls_reg) { asm("mcr p15, 0, %0, c13, c0, 3" : : "r" (val)); diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S index 40db0f9..ae24dd5 100644 --- a/arch/arm/kernel/entry-header.S +++ b/arch/arm/kernel/entry-header.S @@ -292,6 +292,14 @@ .macro restore_user_regs, fast = 0, offset = 0 +#if defined(CONFIG_CPU_32v6K) && !defined(CONFIG_CPU_V6) + @ The TLS register update is deferred until return to user space so we + @ can use it for other things while running in the kernel + get_thread_info r1 + ldr r1, [r1, #TI_TP_VALUE] + mcr p15, 0, r1, c13, c0, 3 @ set TLS register +#endif + uaccess_enable r1, isb=0 #ifndef CONFIG_THUMB2_KERNEL @ ARM mode restore -- 2.7.4