[PATCH 2/3] x86/split_lock: Refactor and export handle_user_split_lock() for KVM

[Sean Christopherson <sean.j.christopherson@xxxxxxxxx>]

From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

In the future, KVM will use handle_user_split_lock() to handle #AC
caused by split lock in guest. Due to the fact that KVM doesn't have
a @regs context and will pre-check EFLAGS.AC, move the EFLAGS.AC check
to do_alignment_check().

Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/include/asm/cpu.h  | 4 ++--
 arch/x86/kernel/cpu/intel.c | 7 ++++---
 arch/x86/kernel/traps.c     | 2 +-
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index ff6f3ca649b3..ff567afa6ee1 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -43,11 +43,11 @@ unsigned int x86_stepping(unsigned int sig);
 #ifdef CONFIG_CPU_SUP_INTEL
 extern void __init cpu_set_core_cap_bits(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_user_split_lock(unsigned long ip);
 #else
 static inline void __init cpu_set_core_cap_bits(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)
+static inline bool handle_user_split_lock(unsigned long ip)
 {
 	return false;
 }
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 9a26e972cdea..7688f51aabdb 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1066,13 +1066,13 @@ static void split_lock_init(void)
 	split_lock_verify_msr(sld_state != sld_off);
 }
 
-bool handle_user_split_lock(struct pt_regs *regs, long error_code)
+bool handle_user_split_lock(unsigned long ip)
 {
-	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
+	if (sld_state == sld_fatal)
 		return false;
 
 	pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
-			    current->comm, current->pid, regs->ip);
+			    current->comm, current->pid, ip);
 
 	/*
 	 * Disable the split lock detection for this task so it can make
@@ -1083,6 +1083,7 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 	set_tsk_thread_flag(current, TIF_SLD);
 	return true;
 }
+EXPORT_SYMBOL_GPL(handle_user_split_lock);
 
 /*
  * This function is called only when switching between tasks with
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d54cffdc7cac..55902c5bf0aa 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -304,7 +304,7 @@ dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
 
 	local_irq_enable();
 
-	if (handle_user_split_lock(regs, error_code))
+	if (!(regs->flags & X86_EFLAGS_AC) && handle_user_split_lock(regs->ip))
 		return;
 
 	do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
-- 
2.24.1