[PATCHv3 1/5] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time

Kirill A. Shutemov
2017-12-04T12:41:38Z

This patch prepare decompression code to boot-time switching between 4-
and 5-level paging.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org> [4.14+]
---
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/head_64.S | 16 ++++++++++++----
arch/x86/boot/compressed/pgtable_64.c | 18 ++++++++++++++++++
3 files changed, 31 insertions(+), 4 deletions(-)
create mode 100644 arch/x86/boot/compressed/pgtable_64.c

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 1e9c322e973a..f25e1530e064 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -80,6 +80,7 @@ vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
ifdef CONFIG_X86_64
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/pagetable.o
vmlinux-objs-y += $(obj)/mem_encrypt.o
+ vmlinux-objs-y += $(obj)/pgtable_64.o
endif

$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 20919b4f3133..fc313e29fe2c 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -305,10 +305,18 @@ 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,
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
new file mode 100644
index 000000000000..eed3a2c3b577
--- /dev/null
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -0,0 +1,18 @@
+#include <asm/processor.h>
+
+int l5_paging_required(void)
+{
+ /* Check i 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;
+}
--
2.15.0