linux-kernel - [PATCHv6 05/16] x86/cpu: Defer CR pinning setup until after EFI initialization

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Message-ID: <20250620135325.3300848-6-kirill.shutemov@linux.intel.com>
Date: Fri, 20 Jun 2025 16:53:13 +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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	x86@...nel.org,
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	Michael Roth <michael.roth@....com>,
	Tony Luck <tony.luck@...el.com>,
	Alexey Kardashevskiy <aik@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jonathan Corbet <corbet@....net>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
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	linux-doc@...r.kernel.org,
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	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv6 05/16] 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.

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 | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4f430be285de..1a779e302872 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 +2531,21 @@ void __init arch_cpu_finalize_init(void)
 
 	/*
 	 * This needs to follow the FPU initializtion, since EFI depends on it.
+	 *
+	 * It also needs to precede the CR pinning setup, because the CR4.LASS
+	 * bit has to be cleared temporarily in order to execute the
+	 * set_virtual_address_map() EFI call, which resides in lower addresses
+	 * and would trip LASS if enabled.
+	 *
+	 * Wrapping efi_enter_virtual_mode() into lass_stac()/clac() is not
+	 * enough because AC flag gates data accesses, but not instruction
+	 * fetch. Clearing the CR4 bit is required.
 	 */
 	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