linux-kernel - [tip:x86/mm] x86/boot/efi: Define __KERNEL32

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Date:   Tue, 13 Jun 2017 03:06:48 -0700
From:   "tip-bot for Kirill A. Shutemov" <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     akpm@...ux-foundation.org, dvlasenk@...hat.com, bp@...en8.de,
        tglx@...utronix.de, luto@...capital.net, jpoimboe@...hat.com,
        torvalds@...ux-foundation.org, brgerst@...il.com, luto@...nel.org,
        hpa@...or.com, dave.hansen@...el.com, linux-kernel@...r.kernel.org,
        peterz@...radead.org, matt@...eblueprint.co.uk,
        kirill.shutemov@...ux.intel.com, mingo@...nel.org
Subject: [tip:x86/mm] x86/boot/efi: Define __KERNEL32_CS GDT on 64-bit
 configurations

Commit-ID:  919a02d1280a3845bac70e6b7891ca070f21a60a
Gitweb:     http://git.kernel.org/tip/919a02d1280a3845bac70e6b7891ca070f21a60a
Author:     Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
AuthorDate: Tue, 6 Jun 2017 14:31:24 +0300
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 13 Jun 2017 08:56:53 +0200

x86/boot/efi: Define __KERNEL32_CS GDT on 64-bit configurations

We would need to switch temporarily to compatibility mode during booting
with 5-level paging enabled. It would require 32-bit code segment
descriptor.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-arch@...r.kernel.org
Cc: linux-mm@...ck.org
Link: http://lkml.kernel.org/r/20170606113133.22974-6-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/boot/compressed/eboot.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index b75c20f..c3e869e 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -1046,8 +1046,29 @@ struct boot_params *efi_main(struct efi_config *c,
 	memset((char *)gdt->address, 0x0, gdt->size);
 	desc = (struct desc_struct *)gdt->address;
 
-	/* The first GDT is a dummy and the second is unused. */
-	desc += 2;
+	/* The first GDT is a dummy. */
+	desc++;
+
+	if (IS_ENABLED(CONFIG_X86_64)) {
+		/* __KERNEL32_CS */
+		desc->limit0 = 0xffff;
+		desc->base0 = 0x0000;
+		desc->base1 = 0x0000;
+		desc->type = SEG_TYPE_CODE | SEG_TYPE_EXEC_READ;
+		desc->s = DESC_TYPE_CODE_DATA;
+		desc->dpl = 0;
+		desc->p = 1;
+		desc->limit = 0xf;
+		desc->avl = 0;
+		desc->l = 0;
+		desc->d = SEG_OP_SIZE_32BIT;
+		desc->g = SEG_GRANULARITY_4KB;
+		desc->base2 = 0x00;
+		desc++;
+	} else {
+		/* Second entry is unused on 32-bit */
+		desc++;
+	}
 
 	/* __KERNEL_CS */
 	desc->limit0 = 0xffff;