linux-kernel - [PATCH] x86/kexec: Make kexec work in 5-level paging mode

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Message-Id: <20180129110845.26633-1-kirill.shutemov@linux.intel.com>
Date:   Mon, 29 Jan 2018 14:08:45 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] x86/kexec: Make kexec work in 5-level paging mode

I've missed that we need to change relocate_kernel() to set CR4.LA57
flag if the kernel has 5-level paging enabled.

I avoided to use ifdef CONFIG_X86_5LEVEL here and inferred if we need to
enabled 5-level paging from previous CR4 value. This way the code is
ready for boot-time switching between paging modes.

Fixes: 77ef56e4f0fb ("x86: Enable 5-level paging support via CONFIG_X86_5LEVEL=y")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reported-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 307d3bac5f04..11eda21eb697 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -68,6 +68,9 @@ relocate_kernel:
 	movq	%cr4, %rax
 	movq	%rax, CR4(%r11)
 
+	/* Save CR4. Required to enable the right paging mode later. */
+	movq	%rax, %r13
+
 	/* zero out flags, and disable interrupts */
 	pushq $0
 	popfq
@@ -126,8 +129,13 @@ identity_mapped:
 	/*
 	 * Set cr4 to a known state:
 	 *  - physical address extension enabled
+	 *  - 5-level paging, if it was enabled before
 	 */
 	movl	$X86_CR4_PAE, %eax
+	testq	$X86_CR4_LA57, %r13
+	jz	1f
+	orl	$X86_CR4_LA57, %eax
+1:
 	movq	%rax, %cr4
 
 	jmp 1f
-- 
2.15.1