[06/10] x86: efi: Stop using UEFI-provided %gs for percpu storage

Commit Message

Varad Gautam April 12, 2022, 5:32 p.m. UTC

UEFI tests do not update MSR_GS_BASE during bringup, and continue
using the GS_BASE set up by the UEFI implementation for percpu
storage.

Update this MSR during setup_segments64() to allow storing percpu
data at a sane location reserved by the testcase, and ensure that
this happens before any operation that ends up storing to the percpu
space.

Signed-off-by: Varad Gautam <[e-mail]>
---
 lib/x86/setup.c      | 9 ++++++---
 x86/efi/efistart64.S | 7 +++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

Patch

diff --git a/lib/x86/setup.c b/lib/x86/setup.c
index 7dd6677..5d32d3f 100644
--- a/lib/x86/setup.c
+++ b/lib/x86/setup.c
@@ -170,7 +170,8 @@  void setup_multiboot(struct mbi_bootinfo *bi)
 #ifdef CONFIG_EFI
 
 /* From x86/efi/efistart64.S */
-extern void setup_segments64(void);
+extern void setup_segments64(u64 gs_base);
+extern u8 stacktop;
 
 static efi_status_t setup_memory_allocator(efi_bootinfo_t *efi_bootinfo)
 {
@@ -271,12 +272,14 @@  static void setup_page_table(void)
 static void setup_gdt_tss(void)
 {
 	size_t tss_offset;
+	u64 gs_base;
 
 	/* 64-bit setup_tss does not use the stacktop argument.  */
 	tss_offset = setup_tss(NULL);
 	load_gdt_tss(tss_offset);
 
-	setup_segments64();
+	gs_base = (u64)(&stacktop) - (PAGE_SIZE * (pre_boot_apic_id() + 1));
+	setup_segments64(gs_base);
 }
 
 efi_status_t setup_efi(efi_bootinfo_t *efi_bootinfo)
@@ -318,8 +321,8 @@  efi_status_t setup_efi(efi_bootinfo_t *efi_bootinfo)
 		return status;
 	}
 
-	reset_apic();
 	setup_gdt_tss();
+	reset_apic();
 	setup_idt();
 	load_idt();
 	mask_pic_interrupts();
diff --git a/x86/efi/efistart64.S b/x86/efi/efistart64.S
index cb08230..1c38355 100644
--- a/x86/efi/efistart64.S
+++ b/x86/efi/efistart64.S
@@ -44,6 +44,13 @@  setup_segments64:
 	mov %ax, %gs
 	mov %ax, %ss
 
+	/* Setup percpu base */
+	MSR_GS_BASE = 0xc0000101
+	mov %rdi, %rax
+	mov $0, %edx
+	mov $MSR_GS_BASE, %ecx
+	wrmsr
+
 	/*
 	 * 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