From 08529078d8d9adf689bf39cc38d53979a0869970 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Mon, 4 Dec 2017 15:40:55 +0300 Subject: x86/boot/compressed/64: Detect and handle 5-level paging at boot-time 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 Signed-off-by: Thomas Gleixner Cc: Andi Kleen Cc: stable@vger.kernel.org Cc: Andy Lutomirski Cc: linux-mm@kvack.org Cc: Cyrill Gorcunov Cc: Borislav Petkov Cc: Linus Torvalds Link: https://lkml.kernel.org/r/20171204124059.63515-2-kirill.shutemov@linux.intel.com --- arch/x86/boot/compressed/head_64.S | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'arch/x86/boot/compressed/head_64.S') 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, -- cgit v1.2.1