linux-kernel - [PATCH v2 2/2] x86/split-lock: Remove unused TIF

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Message-Id: <20220310204854.31752-3-tony.luck@intel.com>
Date:   Thu, 10 Mar 2022 12:48:54 -0800
From:   Tony Luck <tony.luck@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH v2 2/2] x86/split-lock: Remove unused TIF_SLD bit

Changes to the "warn" mode of split lock handling mean that
TIF_SLD is never set.

Remove the bit, and the functions that use it.

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/include/asm/cpu.h         |  2 --
 arch/x86/include/asm/thread_info.h |  4 +---
 arch/x86/kernel/cpu/intel.c        | 12 ------------
 arch/x86/kernel/process.c          |  3 ---
 4 files changed, 1 insertion(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 33d41e350c79..e346f5c103b7 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -42,14 +42,12 @@ unsigned int x86_model(unsigned int sig);
 unsigned int x86_stepping(unsigned int sig);
 #ifdef CONFIG_CPU_SUP_INTEL
 extern void __init sld_setup(struct cpuinfo_x86 *c);
-extern void switch_to_sld(unsigned long tifn);
 extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
 extern bool handle_guest_split_lock(unsigned long ip);
 extern void handle_bus_lock(struct pt_regs *regs);
 u8 get_this_hybrid_cpu_type(void);
 #else
 static inline void __init sld_setup(struct cpuinfo_x86 *c) {}
-static inline void switch_to_sld(unsigned long tifn) {}
 static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 {
 	return false;
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index ebec69c35e95..f0cb881c1d69 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -92,7 +92,6 @@ struct thread_info {
 #define TIF_NOCPUID		15	/* CPUID is not accessible in userland */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
 #define TIF_NOTIFY_SIGNAL	17	/* signal notifications exist */
-#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 */
 #define TIF_IO_BITMAP		22	/* uses I/O bitmap */
@@ -116,7 +115,6 @@ struct thread_info {
 #define _TIF_NOCPUID		(1 << TIF_NOCPUID)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
-#define _TIF_SLD		(1 << TIF_SLD)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_IO_BITMAP		(1 << TIF_IO_BITMAP)
 #define _TIF_SPEC_FORCE_UPDATE	(1 << TIF_SPEC_FORCE_UPDATE)
@@ -128,7 +126,7 @@ struct thread_info {
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW_BASE					\
 	(_TIF_NOCPUID | _TIF_NOTSC | _TIF_BLOCKSTEP |		\
-	 _TIF_SSBD | _TIF_SPEC_FORCE_UPDATE | _TIF_SLD)
+	 _TIF_SSBD | _TIF_SPEC_FORCE_UPDATE)
 
 /*
  * Avoid calls to __switch_to_xtra() on UP as STIBP is not evaluated.
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 2536784511e3..7cba84616c20 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1241,18 +1241,6 @@ void handle_bus_lock(struct pt_regs *regs)
 	}
 }
 
-/*
- * This function is called only when switching between tasks with
- * different split-lock detection modes. It sets the MSR for the
- * mode of the new task. This is right most of the time, but since
- * the MSR is shared by hyperthreads on a physical core there can
- * be glitches when the two threads need different modes.
- */
-void switch_to_sld(unsigned long tifn)
-{
-	sld_update_msr(!(tifn & _TIF_SLD));
-}
-
 /*
  * Bits in the IA32_CORE_CAPABILITIES are not architectural, so they should
  * only be trusted if it is confirmed that a CPU model implements a
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 81d8ef036637..47db777da92a 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -686,9 +686,6 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 		/* Enforce MSR update to ensure consistent state */
 		__speculation_ctrl_update(~tifn, tifn);
 	}
-
-	if ((tifp ^ tifn) & _TIF_SLD)
-		switch_to_sld(tifn);
 }
 
 /*
-- 
2.35.1