linux-kernel - [PATCHv11 06/19] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

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Date: Tue, 28 May 2024 12:55:09 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Rick Edgecombe  <rick.p.edgecombe@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Baoquan He <bhe@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	kexec@...ts.infradead.org,
	linux-hyperv@...r.kernel.org,
	linux-acpi@...r.kernel.org,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCHv11 06/19] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

TDX guests run with MCA enabled (CR4.MCE=1b) from the very start. If
that bit is cleared during CR4 register reprogramming during boot or
kexec flows, a #VE exception will be raised which the guest kernel
cannot handle it.

Therefore, make sure the CR4.MCE setting is preserved over kexec too and
avoid raising any #VEs.

The change doesn't affect non-TDX-guest environments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 085eef5c3904..b668a6be4f6f 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -5,6 +5,8 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/stringify.h>
+#include <asm/alternative.h>
 #include <asm/page_types.h>
 #include <asm/kexec.h>
 #include <asm/processor-flags.h>
@@ -143,15 +145,17 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 
 	/*
 	 * Set cr4 to a known state:
-	 *  - physical address extension enabled
 	 *  - 5-level paging, if it was enabled before
+	 *  - Machine check exception on TDX guest, if it was enabled before.
+	 *    Clearing MCE might not be allowed in TDX guests, depending on setup.
+	 *  - physical address extension enabled
 	 */
-	movl	$X86_CR4_PAE, %eax
-	testq	$X86_CR4_LA57, %r13
-	jz	.Lno_la57
-	orl	$X86_CR4_LA57, %eax
-.Lno_la57:
+	movl	$X86_CR4_LA57, %eax
+	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
 
+	/* R13 contains the original CR4 value, read in relocate_kernel() */
+	andl	%r13d, %eax
+	orl	$X86_CR4_PAE, %eax
 	movq	%rax, %cr4
 
 	jmp 1f
-- 
2.43.0