linux-kernel - [PATCH] x86/fpu: Turn WARN_ON in context switch into WARN_ON

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Message-Id: <20170329062605.4970-1-andi@firstfloor.org>
Date:   Tue, 28 Mar 2017 23:26:05 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     x86@...nel.org
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] x86/fpu: Turn WARN_ON in context switch into WARN_ON_FPU

From: Andi Kleen <ak@...ux.intel.com>

copy_xregs_to_kernel checks if the alternatives have been already
patched.

This WARN_ON is always executed in every context switch.

All the other checks in fpu internal.h are WARN_ON_FPU, but
this one is plain WARN_ON. I assume it was forgotten to switch it.

So switch it to WARN_ON_FPU too to avoid some unnecessary code
in the context switch, and a potentially expensive cache line miss for the
global variable.

(or could be removed since if it hasn't triggered by now it probably never will)

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/fpu/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index d4a684997497..ec0c542a91ab 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -340,7 +340,7 @@ static inline void copy_xregs_to_kernel(struct xregs_state *xstate)
 	u32 hmask = mask >> 32;
 	int err;
 
-	WARN_ON(!alternatives_patched);
+	WARN_ON_FPU(!alternatives_patched);
 
 	XSTATE_XSAVE(xstate, lmask, hmask, err);
 
-- 
2.9.3