linux-kernel - [tip: x86/boot] x86/boot/64: Load the final kernel GDT during early boot directly, remove startup

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Date: Wed, 28 Feb 2024 10:11:26 -0000
From: "tip-bot2 for Brian Gerst" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Brian Gerst <brgerst@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, Kees Cook <keescook@...omium.org>,
 Andy Lutomirski <luto@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 "H. Peter Anvin" <hpa@...or.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/boot] x86/boot/64: Load the final kernel GDT during early
 boot directly, remove startup_gdt[]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     11e36b0f7c2150a6453872b79555767b43c846d0
Gitweb:        https://git.kernel.org/tip/11e36b0f7c2150a6453872b79555767b43c846d0
Author:        Brian Gerst <brgerst@...il.com>
AuthorDate:    Mon, 26 Feb 2024 17:05:44 -05:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 28 Feb 2024 11:02:16 +01:00

x86/boot/64: Load the final kernel GDT during early boot directly, remove startup_gdt[]

Instead of loading a duplicate GDT just for early boot, load the kernel
GDT from its physical address.

Signed-off-by: Brian Gerst <brgerst@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Ard Biesheuvel <ardb@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lore.kernel.org/r/20240226220544.70769-1-brgerst@gmail.com
---
 arch/x86/include/asm/desc.h |  1 +
 arch/x86/kernel/head64.c    | 13 ++-----------
 2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index ab97b22..52c0150 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -46,6 +46,7 @@ struct gdt_page {
 } __attribute__((aligned(PAGE_SIZE)));
 
 DECLARE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page);
+DECLARE_INIT_PER_CPU(gdt_page);
 
 /* Provide the original GDT */
 static inline struct desc_struct *get_cpu_gdt_rw(unsigned int cpu)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 72351c3..fd77a26 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -68,15 +68,6 @@ unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
 EXPORT_SYMBOL(vmemmap_base);
 #endif
 
-/*
- * GDT used on the boot CPU before switching to virtual addresses.
- */
-static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
-	[GDT_ENTRY_KERNEL32_CS]         = GDT_ENTRY_INIT(DESC_CODE32, 0, 0xfffff),
-	[GDT_ENTRY_KERNEL_CS]           = GDT_ENTRY_INIT(DESC_CODE64, 0, 0xfffff),
-	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(DESC_DATA64, 0, 0xfffff),
-};
-
 #ifdef CONFIG_X86_5LEVEL
 static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
 {
@@ -589,8 +580,8 @@ void __head startup_64_setup_gdt_idt(void)
 	void *handler = NULL;
 
 	struct desc_ptr startup_gdt_descr = {
-		.address = (unsigned long)&RIP_REL_REF(startup_gdt),
-		.size    = sizeof(startup_gdt) - 1,
+		.address = (unsigned long)&RIP_REL_REF(init_per_cpu_var(gdt_page.gdt)),
+		.size    = GDT_SIZE - 1,
 	};
 
 	/* Load GDT */