[PATCH v4 69/75] x86/head/64: Setup TSS early for secondary CPUs

Joerg Roedel
Tue, 14 Jul 2020 12:09:11 -0000

The #VC exception will trigger very early in head_64.S, when the first
CPUID instruction is executed. When secondary CPUs boot, they already
load the real system IDT, which has the #VC handler configured to use an
IST stack. IST stacks require a TSS to be loaded, so set up the TSS
early for bringing up the secondary CPUs. Use the read-write version of
the per-CPU TSS struct early, until cpu_init() switches to the read-only
mapping.

On the boot CPU the TSS will also be loaded early, but not used as the
the early boot #VC handlers do not use IST stacks.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 arch/x86/kernel/head64.c  | 13 +++++++++++++
 arch/x86/kernel/head_64.S |  5 +++++
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 23d492091f3b..f57eefb1e4ba 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -545,6 +545,19 @@ void __head early_idt_setup_early_handler(unsigned long
descr_addr, unsigned lon
 	}
 }

+void __head early_load_tss(void)
+{
+	struct desc_struct *gdt = (struct desc_struct *)boot_gdt;
+	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
+	tss_desc tss_desc;
+
+	set_tssldt_descriptor(&tss_desc, (unsigned long)tss, DESC_TSS,
+			      __KERNEL_TSS_LIMIT);
+	native_write_gdt_entry(gdt, GDT_ENTRY_TSS, &tss_desc, DESC_TSS);
+
+	asm volatile("ltr %w0"::"q" (GDT_ENTRY_TSS*8));
+}
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 static void __head set_early_idt_handler(gate_desc *idt, int n, void *handler)
 {
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 3bd4c36d1d36..5b577d6bce7a 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -235,6 +235,11 @@ SYM_CODE_START(secondary_startup_64)
 	 */
 	movq initial_stack(%rip), %rsp

+	/* Setup a TSS for early IST handlers - needs %gs to be set up */
+	pushq	%rsi
+	call	early_load_tss
+	popq	%rsi
+
 	/* Load IDT */
 	lidt	idt_descr(%rip)

--
2.27.0