EFI uses kernel_fpu_begin() to conform to the UEFI calling convention.
This specifically requires initializing FCW, whereas no sane 64-bit kernel
code should use legacy 387 operations that reference FCW.
Add KFPU_EFI to make this self-documenting, and use it in the EFI code.
This should enable us to safely change the default semantics of
kernel_fpu_begin() to stop initializing FCW on 64-bit kernels.
Cc: Arnd Bergmann <a...@arndb.de>
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
arch/x86/include/asm/efi.h | 4 ++--
arch/x86/include/asm/fpu/api.h | 7 +++++++
arch/x86/platform/efi/efi_64.c | 2 +-
3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index bc9758ef292e..c60be69a5c82 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -71,7 +71,7 @@ extern unsigned long efi_fw_vendor, efi_config_table;
#ifdef CONFIG_X86_32
#define arch_efi_call_virt_setup() \
({ \
- kernel_fpu_begin(); \
+ kernel_fpu_begin_mask(KFPU_EFI); \
firmware_restrict_branch_speculation_start(); \
})
@@ -107,7 +107,7 @@ struct efi_scratch {
#define arch_efi_call_virt_setup() \
({ \
efi_sync_low_kernel_mappings(); \
- kernel_fpu_begin(); \
+ kernel_fpu_begin_mask(KFPU_EFI); \
firmware_restrict_branch_speculation_start(); \
efi_switch_mm(&efi_mm); \
})
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 133907a200ef..e95a06845443 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -25,6 +25,13 @@
#define KFPU_XYZMM _BITUL(1) /* MXCSR will be initialized */
#define KFPU_MMX 0 /* nothing gets initialized */
+/*
+ * The UEFI calling convention (UEFI spec 2.3.2 and 2.3.4) requires
+ * that FCW (32-bit and 64-bit) and MXCSR (64-bit) must be initialized
+ * prior to calling UEFI code.
+ */
+#define KFPU_EFI (KFPU_387 | KFPU_XYZMM)
+
extern void kernel_fpu_begin_mask(unsigned int kfpu_mask);
extern void kernel_fpu_end(void);
extern bool irq_fpu_usable(void);
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 8f5759df7776..c304c8da862b 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -848,7 +848,7 @@ efi_set_virtual_address_map(unsigned long memory_map_size,
virtual_map);
efi_switch_mm(&efi_mm);
- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_EFI);
/* Disable interrupts around EFI calls: */
local_irq_save(flags);
--
2.29.2
