linux-kernel - [PATCHv7 04/16] x86/cpu: Defer CR pinning setup until after EFI initialization

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Message-ID: <20250625125112.3943745-6-kirill.shutemov@linux.intel.com>
Date: Wed, 25 Jun 2025 15:50:57 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
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	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jonathan Corbet <corbet@....net>,
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	Ingo Molnar <mingo@...nel.org>,
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	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv7 04/16] x86/cpu: Defer CR pinning setup until after EFI initialization

From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>

In order to map the EFI runtime services, set_virtual_address_map()
needs to be called, which resides in the lower half of the address
space. This means that LASS needs to be temporarily disabled around
this call. This can only be done before the CR pinning is set up.

Move CR pinning setup behind the EFI initialization.

Wrapping efi_enter_virtual_mode() into lass_disable/enable_enforcement()
is not enough because AC flag gates data accesses, but not instruction
fetch. Clearing the CR4 bit is required.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/kernel/cpu/common.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4f430be285de..9918121e0adc 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2081,7 +2081,6 @@ static __init void identify_boot_cpu(void)
 	enable_sep_cpu();
 #endif
 	cpu_detect_tlb(&boot_cpu_data);
-	setup_cr_pinning();
 
 	tsx_init();
 	tdx_init();
@@ -2532,10 +2531,14 @@ void __init arch_cpu_finalize_init(void)
 
 	/*
 	 * This needs to follow the FPU initializtion, since EFI depends on it.
+	 *
+	 * EFI twiddles CR4.LASS. Do it before CR pinning.
 	 */
 	if (efi_enabled(EFI_RUNTIME_SERVICES))
 		efi_enter_virtual_mode();
 
+	setup_cr_pinning();
+
 	/*
 	 * Ensure that access to the per CPU representation has the initial
 	 * boot CPU configuration.
-- 
2.47.2