[PATCH 25/62] x86/head/64: Install boot GDT

[Joerg Roedel]

From: Joerg Roedel <jroedel@xxxxxxx>

Handling exceptions during boot requires a working GDT. The kernel GDT
is not yet ready for use, so install a temporary boot GDT.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
 arch/x86/kernel/head_64.S | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4bbc770af632..5a3cde971cb7 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -72,6 +72,20 @@ SYM_CODE_START_NOALIGN(startup_64)
 	/* Set up the stack for verify_cpu(), similar to initial_stack below */
 	leaq	(__end_init_task - SIZEOF_PTREGS)(%rip), %rsp
 
+	/* Setup boot GDT descriptor and load boot GDT */
+	leaq	boot_gdt(%rip), %rax
+	movq	%rax, boot_gdt_base(%rip)
+	lgdt	boot_gdt_descr(%rip)
+
+	/* GDT loaded - switch to __KERNEL_CS so IRET works reliably */
+	pushq	$__KERNEL_CS
+	leaq	.Lon_kernel_cs(%rip), %rax
+	pushq	%rax
+	lretq
+
+.Lon_kernel_cs:
+	UNWIND_HINT_EMPTY
+
 	/* Sanitize CPU configuration */
 	call verify_cpu
 
@@ -480,6 +494,18 @@ SYM_DATA_LOCAL(early_gdt_descr_base,	.quad INIT_PER_CPU_VAR(gdt_page))
 SYM_DATA(phys_base, .quad 0x0)
 EXPORT_SYMBOL(phys_base)
 
+/* Boot GDT used when kernel addresses are not mapped yet */
+SYM_DATA_LOCAL(boot_gdt_descr,		.word boot_gdt_end - boot_gdt)
+SYM_DATA_LOCAL(boot_gdt_base,		.quad 0)
+SYM_DATA_START(boot_gdt)
+	.quad	0
+	.quad   0x00cf9a000000ffff      /* __KERNEL32_CS */
+	.quad   0x00af9a000000ffff      /* __KERNEL_CS */
+	.quad   0x00cf92000000ffff      /* __KERNEL_DS */
+	.quad   0x0080890000000000      /* TS descriptor */
+	.quad   0x0000000000000000      /* TS continued */
+SYM_DATA_END_LABEL(boot_gdt, SYM_L_LOCAL, boot_gdt_end)
+
 #include "../../x86/xen/xen-head.S"
 
 	__PAGE_ALIGNED_BSS
-- 
2.17.1