Merge tag 'x86_fpu_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 FPU updates from Borislav Petkov:
 "x86 fpu usage optimization and cleanups:

   - make 64-bit kernel code which uses 387 insns request a x87 init
     (FNINIT) explicitly when using the FPU

   - misc cleanups"

* tag 'x86_fpu_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fpu/xstate: Use sizeof() instead of a constant
  x86/fpu/64: Don't FNINIT in kernel_fpu_begin()
  x86/fpu: Make the EFI FPU calling convention explicit

4 files changed, 36 insertions, 8 deletions

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 627347af343a..4d0b126835b8 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -69,17 +69,33 @@ extern unsigned long efi_mixed_mode_stack_pa;
 		#f " called with too many arguments (" #p ">" #n ")");	\
 })
 
+static inline void efi_fpu_begin(void)
+{
+	/*
+	 * The UEFI calling convention (UEFI spec 2.3.2 and 2.3.4) requires
+	 * that FCW and MXCSR (64-bit) must be initialized prior to calling
+	 * UEFI code.  (Oddly the spec does not require that the FPU stack
+	 * be empty.)
+	 */
+	kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);
+}
+
+static inline void efi_fpu_end(void)
+{
+	kernel_fpu_end();
+}
+
 #ifdef CONFIG_X86_32
 #define arch_efi_call_virt_setup()					\
 ({									\
-	kernel_fpu_begin();						\
+	efi_fpu_begin();						\
 	firmware_restrict_branch_speculation_start();			\
 })
 
 #define arch_efi_call_virt_teardown()					\
 ({									\
 	firmware_restrict_branch_speculation_end();			\
-	kernel_fpu_end();						\
+	efi_fpu_end();							\
 })
 
 #define arch_efi_call_virt(p, f, args...)	p->f(args)
@@ -98,7 +114,7 @@ extern asmlinkage u64 __efi_call(void *fp, ...);
 #define arch_efi_call_virt_setup()					\
 ({									\
 	efi_sync_low_kernel_mappings();					\
-	kernel_fpu_begin();						\
+	efi_fpu_begin();						\
 	firmware_restrict_branch_speculation_start();			\
 	efi_enter_mm();							\
 })
@@ -110,7 +126,7 @@ extern asmlinkage u64 __efi_call(void *fp, ...);
 ({									\
 	efi_leave_mm();							\
 	firmware_restrict_branch_speculation_end();			\
-	kernel_fpu_end();						\
+	efi_fpu_end();							\
 })
 
 #ifdef CONFIG_KASAN
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 67a4f1cb2aac..ed33a14188f6 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -32,7 +32,19 @@ extern void fpregs_mark_activate(void);
 /* Code that is unaware of kernel_fpu_begin_mask() can use this */
 static inline void kernel_fpu_begin(void)
 {
+#ifdef CONFIG_X86_64
+	/*
+	 * Any 64-bit code that uses 387 instructions must explicitly request
+	 * KFPU_387.
+	 */
+	kernel_fpu_begin_mask(KFPU_MXCSR);
+#else
+	/*
+	 * 32-bit kernel code may use 387 operations as well as SSE2, etc,
+	 * as long as it checks that the CPU has the required capability.
+	 */
 	kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);
+#endif
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 5d8047441a0a..683749b80ae2 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -167,14 +167,14 @@ void fpstate_sanitize_xstate(struct fpu *fpu)
 		fx->fop = 0;
 		fx->rip = 0;
 		fx->rdp = 0;
-		memset(&fx->st_space[0], 0, 128);
+		memset(fx->st_space, 0, sizeof(fx->st_space));
 	}
 
 	/*
 	 * SSE is in init state
 	 */
 	if (!(xfeatures & XFEATURE_MASK_SSE))
-		memset(&fx->xmm_space[0], 0, 256);
+		memset(fx->xmm_space, 0, sizeof(fx->xmm_space));
 
 	/*
 	 * First two features are FPU and SSE, which above we handled
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index bf85db683af4..1b82d77019b1 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -834,7 +834,7 @@ efi_set_virtual_address_map(unsigned long memory_map_size,
 							 virtual_map);
 	efi_enter_mm();
 
-	kernel_fpu_begin();
+	efi_fpu_begin();
 
 	/* Disable interrupts around EFI calls: */
 	local_irq_save(flags);
@@ -843,7 +843,7 @@ efi_set_virtual_address_map(unsigned long memory_map_size,
 			  descriptor_version, virtual_map);
 	local_irq_restore(flags);
 
-	kernel_fpu_end();
+	efi_fpu_end();
 
 	/* grab the virtually remapped EFI runtime services table pointer */
 	efi.runtime = READ_ONCE(systab->runtime);