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From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
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Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
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	Rick Edgecombe  <rick.p.edgecombe@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kalra, Ashish" <ashish.kalra@amd.com>,
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	"Huang, Kai" <kai.huang@intel.com>,
	Baoquan He <bhe@redhat.com>,
	kexec@lists.infradead.org,
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	linux-kernel@vger.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCHv10 05/18] x86/kexec: Keep CR4.MCE set during kexec for TDX guest
Date: Tue,  9 Apr 2024 14:29:57 +0300
Message-ID: <20240409113010.465412-6-kirill.shutemov@linux.intel.com>
In-Reply-To: <20240409113010.465412-1-kirill.shutemov@linux.intel.com>
References: <20240409113010.465412-1-kirill.shutemov@linux.intel.com>
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Depending on setup, TDX guests might be allowed to clear CR4.MCE.
Attempt to clear it leads to #VE.

Use alternatives to keep the flag during kexec for TDX guests.

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

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..8e2037d78a1f 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>
@@ -145,11 +147,17 @@ 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 allowed in TDX guests, depending on setup.
 	 */
 	movl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
+1:
+	testq	$X86_CR4_MCE, %r13
+	jz	1f
+	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
 1:
 	movq	%rax, %cr4
 
-- 
2.43.0