4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20171204124059.63515-2-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
+}
--
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