linux-kernel - [PATCH 5/6] arch: x86: Reclaim TIF

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Date:   Tue, 28 Jul 2020 16:22:28 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     luto@...nel.org, tglx@...utronix.de
Cc:     keescook@...omium.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com
Subject: [PATCH 5/6] arch: x86: Reclaim TIF_IA32 flag

Dropping this as a TIF flag is interesting given the pressure over x86
remaining x86 flags, plus considering the current common entry code,
reducing arch-specific flags is a good thing.

Notice that no path really relies on TIF_IA32 as part of a critical
path, therefore the cost of checking another field in thread_info
shouldn't be a problem.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
---
 arch/x86/include/asm/thread_info.h | 4 +---
 arch/x86/kernel/process_64.c       | 3 ---
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 698feefd5f5f..aa7d27054a8a 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -99,7 +99,6 @@ struct thread_info {
 #define TIF_NEED_FPU_LOAD	14	/* load FPU on return to userspace */
 #define TIF_NOCPUID		15	/* CPUID is not accessible in userland */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
-#define TIF_IA32		17	/* IA32 compatibility process */
 #define TIF_SLD			18	/* Restore split lock detection on context switch */
 #define TIF_MEMDIE		20	/* is terminating due to OOM killer */
 #define TIF_POLLING_NRFLAG	21	/* idle is polling for TIF_NEED_RESCHED */
@@ -129,7 +128,6 @@ struct thread_info {
 #define _TIF_NEED_FPU_LOAD	(1 << TIF_NEED_FPU_LOAD)
 #define _TIF_NOCPUID		(1 << TIF_NOCPUID)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
-#define _TIF_IA32		(1 << TIF_IA32)
 #define _TIF_SLD		(1 << TIF_SLD)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_IO_BITMAP		(1 << TIF_IO_BITMAP)
@@ -245,7 +243,7 @@ extern void arch_setup_new_exec(void);
 #define arch_setup_new_exec arch_setup_new_exec
 #endif	/* !__ASSEMBLY__ */
 
-#define TASK_IA32(tsk) test_tsk_thread_flag(tsk, TIF_IA32)
+#define TASK_IA32(tsk) (task_thread_info(tsk)->psabi == PSABI_IA32)
 #define TASK_X32(tsk) test_tsk_thread_flag(tsk, TIF_X32)
 
 #endif /* _ASM_X86_THREAD_INFO_H */
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index aea2c03e8a5d..75059c9de829 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -533,7 +533,6 @@ void set_personality_64bit(void)
 
 	/* Make sure to be in 64bit mode */
 	current_thread_info()->psabi = PSABI_IA64;
-	clear_thread_flag(TIF_IA32);
 	clear_thread_flag(TIF_ADDR32);
 	clear_thread_flag(TIF_X32);
 	/* Pretend that this comes from a 64bit execve */
@@ -555,7 +554,6 @@ static void __set_personality_x32(void)
 {
 #ifdef CONFIG_X86_X32
 	current_thread_info()->psabi = PSABI_X32;
-	clear_thread_flag(TIF_IA32);
 	set_thread_flag(TIF_X32);
 	if (current->mm)
 		current->mm->context.ia32_compat = PSABI_X32;
@@ -577,7 +575,6 @@ static void __set_personality_ia32(void)
 {
 #ifdef CONFIG_IA32_EMULATION
 	current_thread_info()->psabi = PSABI_IA32;
-	set_thread_flag(TIF_IA32);
 	clear_thread_flag(TIF_X32);
 	if (current->mm)
 		current->mm->context.ia32_compat = PSABI_IA32;
-- 
2.27.0