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

Joerg Roedel
2020-07-14T12:12:04Z

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 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@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