From ff38bbbac39eade57e4672f9601f602ed8d4b493 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Sun, 12 Jan 2025 13:56:46 +0100 Subject: [PATCH] x86/efi/mixed: Factor out and clean up long mode entry Entering long mode involves setting the EFER_LME and CR4.PAE bits before enabling paging by setting CR0.PG bit. It also involves disabling interrupts, given that the firmware's 32-bit IDT becomes invalid as soon as the CPU transitions into long mode. Reloading the CR3 register is not necessary at boot time, given that the EFI firmware as well as the kernel's EFI stub use a 1:1 mapping of the 32-bit addressable memory in the system. Break out this code into a separate helper for clarity, and so that it can be reused in a subsequent patch. Acked-by: Ingo Molnar Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/efi_mixed.S | 29 ++++++++++++++-------------- 1 file changed, 15 insertions(+), 14 deletions(-) diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S index b7886e2591fcf..0b6b37b08f82f 100644 --- a/arch/x86/boot/compressed/efi_mixed.S +++ b/arch/x86/boot/compressed/efi_mixed.S @@ -170,10 +170,6 @@ SYM_FUNC_START_LOCAL(efi_enter32) movl %edx, %gs movl %edx, %ss - /* Reload pgtables */ - movl %cr3, %eax - movl %eax, %cr3 - /* Disable paging */ movl %cr0, %eax btrl $X86_CR0_PG_BIT, %eax @@ -199,30 +195,35 @@ SYM_FUNC_START_LOCAL(efi_enter32) lidtl 16(%ebx) lgdtl (%ebx) + xorl %eax, %eax + lldt %ax + + call efi32_enable_long_mode + + pushl $__KERNEL_CS + pushl %ebp + lret +SYM_FUNC_END(efi_enter32) + +SYM_FUNC_START_LOCAL(efi32_enable_long_mode) movl %cr4, %eax btsl $(X86_CR4_PAE_BIT), %eax movl %eax, %cr4 - movl %cr3, %eax - movl %eax, %cr3 - movl $MSR_EFER, %ecx rdmsr btsl $_EFER_LME, %eax wrmsr - xorl %eax, %eax - lldt %ax - - pushl $__KERNEL_CS - pushl %ebp + /* Disable interrupts - the firmware's IDT does not work in long mode */ + cli /* Enable paging */ movl %cr0, %eax btsl $X86_CR0_PG_BIT, %eax movl %eax, %cr0 - lret -SYM_FUNC_END(efi_enter32) + ret +SYM_FUNC_END(efi32_enable_long_mode) /* * This is the common EFI stub entry point for mixed mode. -- 2.47.2