pending/x86-fpu-don-t-export-__kernel_fpu_-begin-end.patch

   1 From 12209993e98c5fa1855c467f22a24e3d5b8be205 Mon Sep 17 00:00:00 2001
   2 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
   3 Date: Thu, 29 Nov 2018 16:02:10 +0100
   4 Subject: x86/fpu: Don't export __kernel_fpu_{begin,end}()
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   8
   9 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
  10
  11 commit 12209993e98c5fa1855c467f22a24e3d5b8be205 upstream.
  12
  13 There is one user of __kernel_fpu_begin() and before invoking it,
  14 it invokes preempt_disable(). So it could invoke kernel_fpu_begin()
  15 right away. The 32bit version of arch_efi_call_virt_setup() and
  16 arch_efi_call_virt_teardown() does this already.
  17
  18 The comment above *kernel_fpu*() claims that before invoking
  19 __kernel_fpu_begin() preemption should be disabled and that KVM is a
  20 good example of doing it. Well, KVM doesn't do that since commit
  21
  22   f775b13eedee2 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run")
  23
  24 so it is not an example anymore.
  25
  26 With EFI gone as the last user of __kernel_fpu_{begin|end}(), both can
  27 be made static and not exported anymore.
  28
  29 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
  30 Signed-off-by: Borislav Petkov <bp@suse.de>
  31 Reviewed-by: Rik van Riel <riel@surriel.com>
  32 Cc: "H. Peter Anvin" <hpa@zytor.com>
  33 Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
  34 Cc: Andy Lutomirski <luto@kernel.org>
  35 Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
  36 Cc: Dave Hansen <dave.hansen@linux.intel.com>
  37 Cc: Ingo Molnar <mingo@redhat.com>
  38 Cc: Nicolai Stange <nstange@suse.de>
  39 Cc: Paolo Bonzini <pbonzini@redhat.com>
  40 Cc: Radim Krčmář <rkrcmar@redhat.com>
  41 Cc: Thomas Gleixner <tglx@linutronix.de>
  42 Cc: kvm ML <kvm@vger.kernel.org>
  43 Cc: linux-efi <linux-efi@vger.kernel.org>
  44 Cc: x86-ml <x86@kernel.org>
  45 Link: https://lkml.kernel.org/r/20181129150210.2k4mawt37ow6c2vq@linutronix.de
  46 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  47
  48 diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
  49 index eea40d52ca78..45864898f7e5 100644
  50 --- a/arch/x86/include/asm/efi.h
  51 +++ b/arch/x86/include/asm/efi.h
  52 @@ -82,8 +82,7 @@ struct efi_scratch {
  53  #define arch_efi_call_virt_setup()                                     \
  54  ({                                                                     \
  55         efi_sync_low_kernel_mappings();                                 \
  56 -       preempt_disable();                                              \
  57 -       __kernel_fpu_begin();                                           \
  58 +       kernel_fpu_begin();                                             \
  59         firmware_restrict_branch_speculation_start();                   \
  60                                                                         \
  61         if (!efi_enabled(EFI_OLD_MEMMAP))                               \
  62 @@ -99,8 +98,7 @@ struct efi_scratch {
  63                 efi_switch_mm(efi_scratch.prev_mm);                     \
  64                                                                         \
  65         firmware_restrict_branch_speculation_end();                     \
  66 -       __kernel_fpu_end();                                             \
  67 -       preempt_enable();                                               \
  68 +       kernel_fpu_end();                                               \
  69  })
  70
  71  extern void __iomem *__init efi_ioremap(unsigned long addr, unsigned long size,
  72 diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
  73 index a9caac9d4a72..b56d504af654 100644
  74 --- a/arch/x86/include/asm/fpu/api.h
  75 +++ b/arch/x86/include/asm/fpu/api.h
  76 @@ -12,17 +12,12 @@
  77  #define _ASM_X86_FPU_API_H
  78
  79  /*
  80 - * Careful: __kernel_fpu_begin/end() must be called with preempt disabled
  81 - * and they don't touch the preempt state on their own.
  82 - * If you enable preemption after __kernel_fpu_begin(), preempt notifier
  83 - * should call the __kernel_fpu_end() to prevent the kernel/user FPU
  84 - * state from getting corrupted. KVM for example uses this model.
  85 - *
  86 - * All other cases use kernel_fpu_begin/end() which disable preemption
  87 - * during kernel FPU usage.
  88 + * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
  89 + * disables preemption so be careful if you intend to use it for long periods
  90 + * of time.
  91 + * If you intend to use the FPU in softirq you need to check first with
  92 + * irq_fpu_usable() if it is possible.
  93   */
  94 -extern void __kernel_fpu_begin(void);
  95 -extern void __kernel_fpu_end(void);
  96  extern void kernel_fpu_begin(void);
  97  extern void kernel_fpu_end(void);
  98  extern bool irq_fpu_usable(void);
  99 diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
 100 index 2ea85b32421a..2e5003fef51a 100644
 101 --- a/arch/x86/kernel/fpu/core.c
 102 +++ b/arch/x86/kernel/fpu/core.c
 103 @@ -93,7 +93,7 @@ bool irq_fpu_usable(void)
 104  }
 105  EXPORT_SYMBOL(irq_fpu_usable);
 106
 107 -void __kernel_fpu_begin(void)
 108 +static void __kernel_fpu_begin(void)
 109  {
 110         struct fpu *fpu = &current->thread.fpu;
 111
 112 @@ -111,9 +111,8 @@ void __kernel_fpu_begin(void)
 113                 __cpu_invalidate_fpregs_state();
 114         }
 115  }
 116 -EXPORT_SYMBOL(__kernel_fpu_begin);
 117
 118 -void __kernel_fpu_end(void)
 119 +static void __kernel_fpu_end(void)
 120  {
 121         struct fpu *fpu = &current->thread.fpu;
 122
 123 @@ -122,7 +121,6 @@ void __kernel_fpu_end(void)
 124
 125         kernel_fpu_enable();
 126  }
 127 -EXPORT_SYMBOL(__kernel_fpu_end);
 128
 129  void kernel_fpu_begin(void)
 130  {