linux-kernel - [RFC PATCH 1/2] Revert "x86/kexec/64: Prevent kexec from 5-level paging to a 4-level only kernel"

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Date: Fri,  1 Mar 2024 19:56:17 +0100
From: Borislav Petkov <bp@...en8.de>
To: Baoquan He <bhe@...hat.com>
Cc: X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 1/2] Revert "x86/kexec/64: Prevent kexec from 5-level paging to a 4-level only kernel"

From: "Borislav Petkov (AMD)" <bp@...en8.de>

This reverts commit ee338b9ee2822e65a85750da6129946c14962410.

This whole dynamic switching support is silly. I don't see a use case
where one would use an old kernel with CONFIG_X86_5LEVEL disabled to
kexec into. I.e., you use pretty much the same kernel.

But I'm open to corrections.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/kernel/kexec-bzimage64.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index cde167b0ea92..4f2e47338b7f 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -375,11 +375,6 @@ static int bzImage64_probe(const char *buf, unsigned long len)
 		return ret;
 	}
 
-	if (!(header->xloadflags & XLF_5LEVEL) && pgtable_l5_enabled()) {
-		pr_err("bzImage cannot handle 5-level paging mode.\n");
-		return ret;
-	}
-
 	/* I've got a bzImage */
 	pr_debug("It's a relocatable bzImage64\n");
 	ret = 0;
-- 
2.43.0