linux-kernel - [PATCH 4.14 037/178] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time

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Message-Id: <20171218152922.093379611@linuxfoundation.org>
Date:   Mon, 18 Dec 2017 16:47:53 +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,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>, linux-mm@...ck.org,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 037/178] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time

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

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

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

commit 08529078d8d9adf689bf39cc38d53979a0869970 upstream.

Prerequisite for fixing the current problem of instantaneous reboots when a
5-level paging kernel is booted on 4-level paging hardware.

At the same time this change prepares the decompression code to boot-time
switching between 4- and 5-level paging.

[ tglx: Folded the GCC < 5 fix. ]

Fixes: 77ef56e4f0fb ("x86: Enable 5-level paging support via CONFIG_X86_5LEVEL=y")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: linux-mm@...ck.org
Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lkml.kernel.org/r/20171204124059.63515-2-kirill.shutemov@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/boot/compressed/Makefile     |    1 +
 arch/x86/boot/compressed/head_64.S    |   16 ++++++++++++----
 arch/x86/boot/compressed/pgtable_64.c |   28 ++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 4 deletions(-)

--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -78,6 +78,7 @@ vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $
 vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
 ifdef CONFIG_X86_64
 	vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/pagetable.o
+	vmlinux-objs-y += $(obj)/pgtable_64.o
 endif
 
 $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -289,10 +289,18 @@ ENTRY(startup_64)
 	leaq	boot_stack_end(%rbx), %rsp
 
 #ifdef CONFIG_X86_5LEVEL
-	/* Check if 5-level paging has already enabled */
-	movq	%cr4, %rax
-	testl	$X86_CR4_LA57, %eax
-	jnz	lvl5
+	/*
+	 * Check if we need to enable 5-level paging.
+	 * RSI holds real mode data and need to be preserved across
+	 * a function call.
+	 */
+	pushq	%rsi
+	call	l5_paging_required
+	popq	%rsi
+
+	/* If l5_paging_required() returned zero, we're done here. */
+	cmpq	$0, %rax
+	je	lvl5
 
 	/*
 	 * At this point we are in long mode with 4-level paging enabled,
--- /dev/null
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -0,0 +1,28 @@
+#include <asm/processor.h>
+
+/*
+ * __force_order is used by special_insns.h asm code to force instruction
+ * serialization.
+ *
+ * It is not referenced from the code, but GCC < 5 with -fPIE would fail
+ * due to an undefined symbol. Define it to make these ancient GCCs work.
+ */
+unsigned long __force_order;
+
+int l5_paging_required(void)
+{
+	/* Check if leaf 7 is supported. */
+
+	if (native_cpuid_eax(0) < 7)
+		return 0;
+
+	/* Check if la57 is supported. */
+	if (!(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31))))
+		return 0;
+
+	/* Check if 5-level paging has already been enabled. */
+	if (native_read_cr4() & X86_CR4_LA57)
+		return 0;
+
+	return 1;
+}