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

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Date:   Mon, 24 Aug 2020 10:54:33 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v6 38/76] x86/head/64: Set CR4.FSGSBASE early

From: Joerg Roedel <jroedel@...e.de>

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@...e.de>
Link: https://lore.kernel.org/r/20200724160336.5435-38-joro@8bytes.org
---
 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