[PATCH v5 32/75] x86/head/64: Load segment registers earlier

Joerg Roedel
2020-07-24T16:07:37Z

Make sure segments are properly set up before setting up an IDT and
doing anything that might cause a #VC exception. This is later needed
for early exception handling.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/head_64.S | 52 +++++++++++++++++++--------------------
1 file changed, 26 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index f958d4e4ee08..057c7bd3eeb6 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -174,6 +174,32 @@ SYM_CODE_START(secondary_startup_64)
*/
lgdt early_gdt_descr(%rip)

+ /* set up data segments */
+ xorl %eax,%eax
+ movl %eax,%ds
+ movl %eax,%ss
+ movl %eax,%es
+
+ /*
+ * We don't really need to load %fs or %gs, but load them anyway
+ * to kill any stale realmode selectors. This allows execution
+ * under VT hardware.
+ */
+ movl %eax,%fs
+ movl %eax,%gs
+
+ /* Set up %gs.
+ *
+ * The base of %gs always points to fixed_percpu_data. If the
+ * stack protector canary is enabled, it is located at %gs:40.
+ * Note that, on SMP, the boot cpu uses init data section until
+ * the per cpu areas are set up.
+ */
+ movl $MSR_GS_BASE,%ecx
+ movl initial_gs(%rip),%eax
+ movl initial_gs+4(%rip),%edx
+ wrmsr
+
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
@@ -201,32 +227,6 @@ SYM_CODE_START(secondary_startup_64)
pushq $0
popfq

- /* set up data segments */
- xorl %eax,%eax
- movl %eax,%ds
- movl %eax,%ss
- movl %eax,%es
-
- /*
- * We don't really need to load %fs or %gs, but load them anyway
- * to kill any stale realmode selectors. This allows execution
- * under VT hardware.
- */
- movl %eax,%fs
- movl %eax,%gs
-
- /* Set up %gs.
- *
- * The base of %gs always points to fixed_percpu_data. If the
- * stack protector canary is enabled, it is located at %gs:40.
- * Note that, on SMP, the boot cpu uses init data section until
- * the per cpu areas are set up.
- */
- movl $MSR_GS_BASE,%ecx
- movl initial_gs(%rip),%eax
- movl initial_gs+4(%rip),%edx
- wrmsr
-
/* rsi is pointer to real mode structure with interesting info.
pass it to C */
movq %rsi, %rdi
--
2.27.0