From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Sat, 10 Feb 2018 04:16:09 +0000 (-0500)
Subject: x86/spectre_v2: Only use IBRS when ibrs_inuse tells us to
X-Git-Tag: v4.1.12-124.31.3~1135
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=79e253dddafcda1d23403e5250526dc4cbd3fc75;p=users%2Fjedix%2Flinux-maple.git

x86/spectre_v2: Only use IBRS when ibrs_inuse tells us to

instead of using it if the CPU has detected that it exists.

This conflicts with retpoline - as when retpoline is enabled
we end up enabling/disabling the IBRS even though we should
not be touching this MSR.

OraBug: 27526563
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
---

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 0d9fa5311f9a..9f60bcbf85ca 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -463,17 +463,17 @@ static __cpuidle void mwait_idle(void)
 			smp_mb(); /* quirk */
 		}
 
-		if (boot_cpu_has(X86_FEATURE_IBRS))
+		if (ibrs_inuse)
 			native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_FEATURE_DISABLE_IBRS);
 
 		__monitor((void *)&current_thread_info()->flags, 0, 0);
 		if (!need_resched()) {
 			__sti_mwait(0, 0);
-			if (boot_cpu_has(X86_FEATURE_IBRS))
+			if (ibrs_inuse)
 				native_wrmsrl(MSR_IA32_SPEC_CTRL,
 				    SPEC_CTRL_FEATURE_ENABLE_IBRS);
 		} else {
-			if (boot_cpu_has(X86_FEATURE_IBRS))
+			if (ibrs_inuse)
 				native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_FEATURE_ENABLE_IBRS);
 			local_irq_enable();
 		}