linux-kernel - [PATCH] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

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Message-Id: <20190206115253.1907-1-kirill.shutemov@linux.intel.com>
Date:   Wed,  6 Feb 2019 14:52:53 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        dave.hansen@...ux.intel.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kyle D Pelton <kyle.d.pelton@...el.com>,
        Wei Huang <wei@...hat.com>
Subject: [PATCH] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

RDMSR in the trampoline code overrides EDX, but we use the register to
indicate if 5-level paging has to enabled. It leads to failure to boot
on a 5-level paging machine.

Preserve EDX on the stack while we are dealing with EFER.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: b677dfae5aa1 ("x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline before returning to long mode")
Reported-by: Kyle D Pelton <kyle.d.pelton@...el.com>
Cc: Wei Huang <wei@...hat.com>
---
 arch/x86/boot/compressed/head_64.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f105ae8651c9..f62e347862cc 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -602,10 +602,12 @@ ENTRY(trampoline_32bit_src)
 3:
 	/* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */
 	pushl	%ecx
+	pushl	%edx
 	movl	$MSR_EFER, %ecx
 	rdmsr
 	btsl	$_EFER_LME, %eax
 	wrmsr
+	popl	%edx
 	popl	%ecx
 
 	/* Enable PAE and LA57 (if required) paging modes */
-- 
2.20.1