[PATCH v5 37/75] x86/head/64: Set CR4.FSGSBASE early

Joerg Roedel
2020-07-24T16:04:40Z

Early exception handling will use rd/wrgsbase in paranoid_entry/exit.
Enable the feature to avoid #UD exceptions on boot APs.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/head_64.S | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 08412f308de3..4622940134a5 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -153,6 +153,13 @@ SYM_CODE_START(secondary_startup_64)
orl $X86_CR4_LA57, %ecx
1:
#endif
+
+ ALTERNATIVE "jmp .Lstartup_write_cr4", "", X86_FEATURE_FSGSBASE
+
+ /* Early exception handling uses FSGSBASE on APs */
+ orl $X86_CR4_FSGSBASE, %ecx
+
+.Lstartup_write_cr4:
movq %rcx, %cr4

/* Setup early boot stage 4-/5-level pagetables. */
--
2.27.0