linux-kernel - [PATCH] x86/MSR: Chop off lower 32-bit value

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Message-ID: <20151031114628.GA8763@pd.tnic>
Date:	Sat, 31 Oct 2015 12:46:28 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] x86/MSR: Chop off lower 32-bit value

On Fri, Oct 30, 2015 at 08:32:53PM +0100, Borislav Petkov wrote:
> On Fri, Oct 30, 2015 at 12:26:42PM -0700, Andy Lutomirski wrote:
> > Want to add that to the patch or make it another patch?
> 
> Yeah, I'll make another one as it is going to document why we're
> explicitly ANDing with 0xffffffffull.

---
>From 89bfdb82447fd5c9f5bd9753040a639364b0c9d2 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@...e.de>
Date: Sat, 31 Oct 2015 12:40:48 +0100
Subject: [PATCH] x86/MSR: Chop off lower 32-bit value

sparse complains that the cast truncates the high bits. But here we
really do know what we're doing and we need the lower 32 bits only as
the @low argument. So make that explicit.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/include/asm/msr.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 77d8b284e4a7..86133827c75c 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -190,7 +190,7 @@ static inline void wrmsr(unsigned msr, unsigned low, unsigned high)
 
 static inline void wrmsrl(unsigned msr, u64 val)
 {
-	native_write_msr(msr, (u32)val, (u32)(val >> 32));
+	native_write_msr(msr, (u32)(val & 0xffffffffULL), (u32)(val >> 32));
 }
 
 /* wrmsr with exception handling */
-- 
2.3.5

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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