From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bp@alien8.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Isaku Yamahata <isaku.yamahata@intel.com>, x86@kernel.org,
        linux-coco@lists.linux.dev, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH 1/2] x86/kexec: Preserve CR4.MCE during kexec
Date:   Tue, 14 Feb 2023 02:48:35 +0300
Message-Id: <20230213234836.3683-2-kirill.shutemov@linux.intel.com>
In-Reply-To: <20230213234836.3683-1-kirill.shutemov@linux.intel.com>
References: <20230213234836.3683-1-kirill.shutemov@linux.intel.com>
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TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
to #VE.

Preserve the flag during kexec.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 4a73351f87f8..18f19dcc40e9 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,8 +145,12 @@ 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
+	 *  - Preserve MCE, if it was set. Clearing MCE may fault in some
+	 *    environments.
 	 */
-	movl	$X86_CR4_PAE, %eax
+	movq	%cr4, %rax
+	andl	$X86_CR4_MCE, %eax
+	orl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
-- 
2.39.1