This patch prepare decompression code to boot-time switching between 4- and 5-level paging. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- arch/x86/boot/compressed/head_64.S | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index b4a5d284391c..cefe4958fda9 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -288,7 +288,29 @@ ENTRY(startup_64) leaq boot_stack_end(%rbx), %rsp #ifdef CONFIG_X86_5LEVEL - /* Check if 5-level paging has already enabled */ + /* Preserve RBX across CPUID */ + movq %rbx, %r8 + + /* Check if leaf 7 is supported */ + xorl %eax, %eax + cpuid + cmpl $7, %eax + jb lvl5 + + /* + * Check if LA57 is supported. + * The feature is enumerated with CPUID.(EAX=07H, ECX=0):ECX[bit 16] + */ + movl $7, %eax + xorl %ecx, %ecx + cpuid + andl $(1 << 16), %ecx + jz lvl5 + + /* Restore RBX */ + movq %r8, %rbx + + /* Check if 5-level paging has already been enabled */ movq %cr4, %rax testl $X86_CR4_LA57, %eax jnz lvl5 @@ -327,6 +349,8 @@ ENTRY(startup_64) pushq %rax lretq lvl5: + /* Restore RBX */ + movq %r8, %rbx #endif /* Zero EFLAGS */ -- 2.14.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
