diff mbox series

[PATCHv6,06/16] efi: Disable LASS around set_virtual_address_map() EFI call

Message ID 20250620135325.3300848-7-kirill.shutemov@linux.intel.com
State New
Headers show
Series x86: Enable Linear Address Space Separation support | expand

Commit Message

Kirill A. Shutemov June 20, 2025, 1:53 p.m. UTC 
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>

Of all the EFI runtime services, set_virtual_address_map() is the only
one that is called at its lower mapping, which LASS prohibits regardless
of EFLAGS.AC setting. The only way to allow this to happen is to disable
LASS in the CR4 register.

Disable LASS around this low address EFI call.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/platform/efi/efi.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)
diff mbox series

Patch

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 463b784499a8..94c335229697 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -825,11 +825,24 @@  static void __init __efi_enter_virtual_mode(void)
 
 	efi_sync_low_kernel_mappings();
 
+	/*
+	 * set_virtual_address_map is the only service located at lower
+	 * addresses, so we have to temporarily disable LASS around it.
+	 * Note that clearing EFLAGS.AC is not enough for this, the whole
+	 * LASS needs to be disabled.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_LASS))
+		cr4_clear_bits(X86_CR4_LASS);
+
 	status = efi_set_virtual_address_map(efi.memmap.desc_size * count,
 					     efi.memmap.desc_size,
 					     efi.memmap.desc_version,
 					     (efi_memory_desc_t *)pa,
 					     efi_systab_phys);
+
+	if (cpu_feature_enabled(X86_FEATURE_LASS))
+		cr4_set_bits(X86_CR4_LASS);
+
 	if (status != EFI_SUCCESS) {
 		pr_err("Unable to switch EFI into virtual mode (status=%lx)!\n",
 		       status);