linux-kernel - [PATCH 2/2] x86/boot/64: Move 5-level paging global variable assignments back

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Date: Fri, 22 Mar 2024 10:41:07 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC: Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, Ingo
 Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Ard
 Biesheuvel <ardb@...nel.org>
Subject: [PATCH 2/2] x86/boot/64: Move 5-level paging global variable assignments back

Commit 63bed9660420 ("x86/startup_64: Defer assignment of 5-level paging
global variables") moved assignment of 5-level global variables to later
in the boot in order to avoid having to use RIP relative addressing in
order to set them. However, when running with 5-level paging and SME
active (mem_encrypt=on), the variables are needed as part of the page
table setup needed to encrypt the kernel (using pgd_none(), p4d_offset(),
etc.). Since the variables haven't been set, the page table manipulation
is done as if 4-level paging is active, causing the system to crash on
boot.

While only a subset of the assignments that were moved need to be set
early, move all of the assignments back into check_la57_support() so that
these assignments aren't spread between two locations. Instead of just
reverting the fix, this uses the new RIP_REL_REF() macro when assigning
the variables.

Fixes: 63bed9660420 ("x86/startup_64: Defer assignment of 5-level paging global variables")
Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/kernel/head64.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 7d2eb035b6a3..a817ed0724d1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -81,6 +81,13 @@ static inline bool check_la57_support(void)
 	if (!(native_read_cr4() & X86_CR4_LA57))
 		return false;

+	RIP_REL_REF(__pgtable_l5_enabled)	= 1;
+	RIP_REL_REF(pgdir_shift)		= 48;
+	RIP_REL_REF(ptrs_per_p4d)		= 512;
+	RIP_REL_REF(page_offset_base)		= __PAGE_OFFSET_BASE_L5;
+	RIP_REL_REF(vmalloc_base)		= __VMALLOC_BASE_L5;
+	RIP_REL_REF(vmemmap_base)		= __VMEMMAP_BASE_L5;
+
 	return true;
 }

@@ -431,15 +438,6 @@ asmlinkage __visible void __init __noreturn x86_64_start_kernel(char * real_mode
 				(__START_KERNEL & PGDIR_MASK)));
 	BUILD_BUG_ON(__fix_to_virt(__end_of_fixed_addresses) <= MODULES_END);

-	if (check_la57_support()) {
-		__pgtable_l5_enabled	= 1;
-		pgdir_shift		= 48;
-		ptrs_per_p4d		= 512;
-		page_offset_base	= __PAGE_OFFSET_BASE_L5;
-		vmalloc_base		= __VMALLOC_BASE_L5;
-		vmemmap_base		= __VMEMMAP_BASE_L5;
-	}
-
 	cr4_init_shadow();

 	/* Kill off the identity-map trampoline */
-- 
2.43.2