[PATCH v6 38/76] x86/head/64: Set CR4.FSGSBASE early

[Joerg Roedel]

From: Joerg Roedel <jroedel@xxxxxxx>

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@xxxxxxx>
Link: https://lore.kernel.org/r/20200724160336.5435-38-joro@xxxxxxxxxx
---
 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. */
-- 
2.28.0