[PATCH v3 70/75] x86/head/64: Setup TSS early for secondary CPUs

Joerg Roedel
2020-04-28T15:17:20Z

From: Joerg Roedel <jroedel@suse.de>

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 be
using an IST stack. IST stacks require a TSS to be loaded, to set up the
TSS early for bringing up the secondary CPUs. Use the RW version of
early, until cpu_init() switches to the RO mapping.

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

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/include/asm/desc.h | 2 ++
arch/x86/kernel/head64.c | 13 +++++++++++++
arch/x86/kernel/head_64.S | 3 +++
3 files changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 30e2a0e863b6..0777b100dc63 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -40,6 +40,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in
desc->l = 0;
}

+extern unsigned char boot_gdt[];
+
extern struct desc_ptr idt_descr;
extern gate_desc idt_table[];
extern const struct desc_ptr debug_idt_descr;
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index d83d59c15548..30a6d09fd9d0 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -523,6 +523,19 @@ void __head early_idt_setup_early_handler(unsigned long physaddr)
}
}

+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));
+}
+
void __head early_idt_setup(unsigned long physbase)
{
gate_desc *idt = fixup_pointer(idt_table, physbase);
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4d84a0c72e36..7f2d5e14db73 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -220,6 +220,9 @@ SYM_CODE_START(secondary_startup_64)
*/
movq initial_stack(%rip), %rsp

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

--
2.17.1