2024-02-26 22:06:18

by Brian Gerst

[permalink] [raw]
Subject: [PATCH v2] x86/boot/64: Load kernel GDT in early boot

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

Signed-off-by: Brian Gerst <[email protected]>
---
v2: Updated to latest tip tree

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 ec95fe44fa3a..62dc9f59ea76 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 72351c3121a6..fd77a266f29d 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 */

base-commit: afb9cce6ad6e808cf659f43925941be96f61b9c9
--
2.43.2



2024-02-27 15:34:52

by Ard Biesheuvel

[permalink] [raw]
Subject: Re: [PATCH v2] x86/boot/64: Load kernel GDT in early boot

On Mon, 26 Feb 2024 at 23:05, Brian Gerst <[email protected]> wrote:
>
> Instead of loading a duplicate GDT just for early boot, load the kernel
> GDT from its physical address.
>
> Signed-off-by: Brian Gerst <[email protected]>
> ---
> v2: Updated to latest tip tree
>

Acked-by: Ard Biesheuvel <[email protected]>

> 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 ec95fe44fa3a..62dc9f59ea76 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 72351c3121a6..fd77a266f29d 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 */
>
> base-commit: afb9cce6ad6e808cf659f43925941be96f61b9c9
> --
> 2.43.2
>

2024-02-28 10:12:08

by tip-bot2 for Jacob Pan

[permalink] [raw]
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 <[email protected]>
AuthorDate: Mon, 26 Feb 2024 17:05:44 -05:00
Committer: Ingo Molnar <[email protected]>
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 <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
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 */