From: Zixuan Wang <zixuanwang@xxxxxxxxxx>
Global Descriptor Table (GDT) defines x86 memory areas, e.g. memory area
for data or code. UEFI has a different GDT compared to KVM-Unit-Tests,
e.g., in UEFI, 3rd GDT entry defines a code segment, while in
KVM-Unit-Tests, 3rd GDT entry is data segment.
Without loading KVM-Unit-Tests GDT, the UEFI GDT is used and is
incompatible with KVM-Unit-Tests. This causes QEMU to silently crash
when a test case changes segments.
This commit fixes this issue by loading KVM-Unit-Tests GDT to replace
UEFI GDT. And since Task State Segment (TSS) is tightly coupled with
GDT, this commit also loads TSS on boot-up.
In this commit, x86/debug.c can run in UEFI and pass all sub-tests.
Co-developed-by: Varad Gautam <varad.gautam@xxxxxxxx>
Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
Signed-off-by: Zixuan Wang <zixuanwang@xxxxxxxxxx>
---
lib/x86/setup.c | 10 ++++++++++
x86/efi/efistart64.S | 42 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)
diff --git a/lib/x86/setup.c b/lib/x86/setup.c
index 8606fe8..f4f9e1b 100644
--- a/lib/x86/setup.c
+++ b/lib/x86/setup.c
@@ -165,10 +165,20 @@ void setup_multiboot(struct mbi_bootinfo *bi)
/* From x86/efi/efistart64.S */
extern void load_idt(void);
+extern void load_gdt_tss(size_t tss_offset);
+
+static void setup_gdt_tss(void)
+{
+ size_t tss_offset;
+
+ tss_offset = setup_tss();
+ load_gdt_tss(tss_offset);
+}
void setup_efi(void)
{
reset_apic();
+ setup_gdt_tss();
setup_idt();
load_idt();
mask_pic_interrupts();
diff --git a/x86/efi/efistart64.S b/x86/efi/efistart64.S
index 41e9185..57299a5 100644
--- a/x86/efi/efistart64.S
+++ b/x86/efi/efistart64.S
@@ -1,7 +1,22 @@
/* Startup code and pre-defined data structures */
+#include "apic-defs.h"
+#include "asm-generic/page.h"
#include "crt0-efi-x86_64.S"
+.globl ring0stacktop
+.globl ring0stacksize
+
+max_cpus = MAX_TEST_CPUS
+ring0stacksize = PAGE_SIZE
+
+.bss
+
+.globl ring0stacktop
+ . = . + ring0stacksize * max_cpus
+ .align 16
+ring0stacktop:
+
.section .init
.code64
.text
@@ -10,3 +25,30 @@
load_idt:
lidtq idt_descr(%rip)
retq
+
+.globl load_gdt_tss
+load_gdt_tss:
+ /* Load GDT */
+ lgdt gdt64_desc(%rip)
+
+ /* Load TSS */
+ mov %rdi, %rax
+ ltr %ax
+
+ /* Update data segments */
+ mov $0x10, %ax /* 3rd entry in gdt64: 32/64-bit data segment */
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %fs
+ mov %ax, %gs
+ mov %ax, %ss
+
+ /*
+ * Update the code segment by putting it on the stack before the return
+ * address, then doing a far return: this will use the new code segment
+ * along with the address.
+ */
+ popq %rdi
+ pushq $0x08 /* 2nd entry in gdt64: 64-bit code segment */
+ pushq %rdi
+ lretq
--
2.33.0
