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Commit 12209993 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Borislav Petkov
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x86/fpu: Don't export __kernel_fpu_{begin,end}() 



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

  f775b13e ("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: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarRik 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
parent 2f2fcc40

arch/x86/include/asm/efi.h

+2 −4
Original line number Diff line number Diff line
@@ -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,

arch/x86/include/asm/fpu/api.h

+5 −10
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/fpu/core.c

+2 −4
Original line number Diff line number Diff line
@@ -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)

{