linux-kernel - [PATCH 4.14 037/167] x86/kexec: Make kexec (mostly) work in 5-level paging mode

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Date:   Wed, 21 Feb 2018 13:47:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.14 037/167] x86/kexec: Make kexec (mostly) work in 5-level paging mode

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

commit 5bf30316991d5bcda046343ee77d823cf16fdd03 upstream.

Currently kexec() will crash when switching into a 5-level paging
enabled kernel.

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

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

With this patch applied, in addition to kexec 4-to-4 which always worked,
we can kexec 4-to-5 and 5-to-5 - while 5-to-4 will need more work.

Reported-by: Baoquan He <bhe@...hat.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Tested-by: Baoquan He <bhe@...hat.com>
Cc: <stable@...r.kernel.org> # v4.14+
Cc: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org
Fixes: 77ef56e4f0fb ("x86: Enable 5-level paging support via CONFIG_X86_5LEVEL=y")
Link: http://lkml.kernel.org/r/20180129110845.26633-1-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/relocate_kernel_64.S |    8 ++++++++
 1 file changed, 8 insertions(+)

--- 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