[MODERATED] [PATCH v6 13/43] MDSv6

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>
Subject:  x86/speculation/mds: Check lazy clear in kernel exit

Add support for only clearing on kernel exit when the per
cpu clear flag is set. This will be the base of lazy
clearing.

Right now this is a nop because mds=full is still default.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/entry/common.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index ffcc24620ec9..cd6e044d6599 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -212,8 +212,12 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 	ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 #endif
 
-	if (static_key_enabled(&force_cpu_clear))
+	if (static_cpu_has(X86_BUG_MDS) &&
+		(static_key_enabled(&force_cpu_clear) ||
+		 __this_cpu_read(clear_cpu_flag))) {
 		clear_cpu();
+		__this_cpu_write(clear_cpu_flag, false);
+	}
 
 	user_enter_irqoff();
 }
-- 
2.17.2