From dada8587068c820ba5e5d09b9c32d8bc28c4dbe6 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 27 Feb 2024 16:19:09 +0100 Subject: [PATCH] x86/startup_64: Simplify CR4 handling in startup code When paging is enabled, the CR4.PAE and CR4.LA57 control bits cannot be changed, and so they can simply be preserved rather than reason about whether or not they need to be set. CR4.MCE should be preserved unless the kernel was built without CONFIG_X86_MCE, in which case it must be cleared. CR4.PSE should be set explicitly, regardless of whether or not it was set before. CR4.PGE is set explicitly, and then cleared and set again after programming CR3 in order to flush TLB entries based on global translations. This makes the first assignment redundant, and can therefore be omitted. So clear PGE by omitting it from the preserve mask, and set it again explicitly after switching to the new page tables. [ bp: Document the exact operation of CR4.PGE ] Signed-off-by: Ard Biesheuvel Signed-off-by: Borislav Petkov (AMD) Tested-by: Tom Lendacky Link: https://lore.kernel.org/r/20240227151907.387873-12-ardb+git@google.com --- arch/x86/kernel/head_64.S | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 86136a78778e..54207e7e5d33 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -185,6 +185,16 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) addq $(init_top_pgt - __START_KERNEL_map), %rax 1: + /* + * Create a mask of CR4 bits to preserve. Omit PGE in order to flush + * global 1:1 translations from the TLBs. + * + * From the SDM: + * "If CR4.PGE is changing from 0 to 1, there were no global TLB + * entries before the execution; if CR4.PGE is changing from 1 to 0, + * there will be no global TLB entries after the execution." + */ + movl $(X86_CR4_PAE | X86_CR4_LA57), %edx #ifdef CONFIG_X86_MCE /* * Preserve CR4.MCE if the kernel will enable #MC support. @@ -193,20 +203,13 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) * configured will crash the system regardless of the CR4.MCE value set * here. */ + orl $X86_CR4_MCE, %edx +#endif movq %cr4, %rcx - andl $X86_CR4_MCE, %ecx -#else - movl $0, %ecx -#endif + andl %edx, %ecx - /* Enable PAE mode, PSE, PGE and LA57 */ - orl $(X86_CR4_PAE | X86_CR4_PSE | X86_CR4_PGE), %ecx -#ifdef CONFIG_X86_5LEVEL - testb $1, __pgtable_l5_enabled(%rip) - jz 1f - orl $X86_CR4_LA57, %ecx -1: -#endif + /* Even if ignored in long mode, set PSE uniformly on all logical CPUs. */ + btsl $X86_CR4_PSE_BIT, %ecx movq %rcx, %cr4 /* Setup early boot stage 4-/5-level pagetables. */ @@ -223,14 +226,10 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) movq %rax, %cr3 /* - * Do a global TLB flush after the CR3 switch to make sure the TLB - * entries from the identity mapping are flushed. + * Set CR4.PGE to re-enable global translations. */ - movq %cr4, %rcx - movq %rcx, %rax - xorq $X86_CR4_PGE, %rcx + btsl $X86_CR4_PGE_BIT, %ecx movq %rcx, %cr4 - movq %rax, %cr4 /* Ensure I am executing from virtual addresses */ movq $1f, %rax