x86/fpu: Don't export __kernel_fpu_{begin,end}()

Sebastian Andrzej Siewior · suryasaimadhu · commit 12209993e98c · 2018-12-04T12:37:28.000+01:00
There is one user of __kernel_fpu_begin() and before invoking it, it invokes preempt_disable(). So it could invoke kernel_fpu_begin() right away. The 32bit version of arch_efi_call_virt_setup() and arch_efi_call_virt_teardown() does this already. The comment above *kernel_fpu*() claims that before invoking __kernel_fpu_begin() preemption should be disabled and that KVM is a good example of doing it. Well, KVM doesn't do that since commit f775b13 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run") so it is not an example anymore. With EFI gone as the last user of __kernel_fpu_{begin|end}(), both can be made static and not exported anymore. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Rik van Riel <riel@surriel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Nicolai Stange <nstange@suse.de> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kvm ML <kvm@vger.kernel.org> Cc: linux-efi <linux-efi@vger.kernel.org> Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20181129150210.2k4mawt37ow6c2vq@linutronix.de
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
@@ -82,8 +82,7 @@ struct efi_scratch {
 #define arch_efi_call_virt_setup()					\
 ({									\
 	efi_sync_low_kernel_mappings();					\
-	preempt_disable();						\
-	__kernel_fpu_begin();						\
+	kernel_fpu_begin();						\
 	firmware_restrict_branch_speculation_start();			\
 									\
 	if (!efi_enabled(EFI_OLD_MEMMAP))				\
@@ -99,8 +98,7 @@ struct efi_scratch {
 		efi_switch_mm(efi_scratch.prev_mm);			\
 									\
 	firmware_restrict_branch_speculation_end();			\
-	__kernel_fpu_end();						\
-	preempt_enable();						\
+	kernel_fpu_end();						\
 })
 
 extern void __iomem *__init efi_ioremap(unsigned long addr, unsigned long size,
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
@@ -12,17 +12,12 @@
 #define _ASM_X86_FPU_API_H
 
 /*
- * Careful: __kernel_fpu_begin/end() must be called with preempt disabled
- * and they don't touch the preempt state on their own.
- * If you enable preemption after __kernel_fpu_begin(), preempt notifier
- * should call the __kernel_fpu_end() to prevent the kernel/user FPU
- * state from getting corrupted. KVM for example uses this model.
- *
- * All other cases use kernel_fpu_begin/end() which disable preemption
- * during kernel FPU usage.
+ * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
+ * disables preemption so be careful if you intend to use it for long periods
+ * of time.
+ * If you intend to use the FPU in softirq you need to check first with
+ * irq_fpu_usable() if it is possible.
  */
-extern void __kernel_fpu_begin(void);
-extern void __kernel_fpu_end(void);
 extern void kernel_fpu_begin(void);
 extern void kernel_fpu_end(void);
 extern bool irq_fpu_usable(void);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
@@ -93,7 +93,7 @@ bool irq_fpu_usable(void)
 }
 EXPORT_SYMBOL(irq_fpu_usable);
 
-void __kernel_fpu_begin(void)
+static void __kernel_fpu_begin(void)
 {
 	struct fpu *fpu = &current->thread.fpu;
 
@@ -111,9 +111,8 @@ void __kernel_fpu_begin(void)
 		__cpu_invalidate_fpregs_state();
 	}
 }
-EXPORT_SYMBOL(__kernel_fpu_begin);
 
-void __kernel_fpu_end(void)
+static void __kernel_fpu_end(void)
 {
 	struct fpu *fpu = &current->thread.fpu;
 
@@ -122,7 +121,6 @@ void __kernel_fpu_end(void)
 
 	kernel_fpu_enable();
 }
-EXPORT_SYMBOL(__kernel_fpu_end);
 
 void kernel_fpu_begin(void)
 {

Original file line number	Diff line number	Diff line change
`@@ -93,7 +93,7 @@ bool irq_fpu_usable(void)`
`93`	`93`	`}`
`94`	`94`	`EXPORT_SYMBOL(irq_fpu_usable);`
`95`	`95`
`96`		`-void __kernel_fpu_begin(void)`
	`96`	`+static void __kernel_fpu_begin(void)`
`97`	`97`	`{`
`98`	`98`	`struct fpu *fpu = &current->thread.fpu;`
`99`	`99`
`@@ -111,9 +111,8 @@ void __kernel_fpu_begin(void)`
`111`	`111`	`__cpu_invalidate_fpregs_state();`
`112`	`112`	`}`
`113`	`113`	`}`
`114`		`-EXPORT_SYMBOL(__kernel_fpu_begin);`
`115`	`114`
`116`		`-void __kernel_fpu_end(void)`
	`115`	`+static void __kernel_fpu_end(void)`
`117`	`116`	`{`
`118`	`117`	`struct fpu *fpu = &current->thread.fpu;`
`119`	`118`
`@@ -122,7 +121,6 @@ void __kernel_fpu_end(void)`
`122`	`121`
`123`	`122`	`kernel_fpu_enable();`
`124`	`123`	`}`
`125`		`-EXPORT_SYMBOL(__kernel_fpu_end);`
`126`	`124`
`127`	`125`	`void kernel_fpu_begin(void)`
`128`	`126`	`{`