linux-kernel - [tip:x86/fpu] x86/fpu: Don't export __kernel_fpu

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Message-ID: <tip-7d79adb87fa79e4a4c59424fd5b5a922861fc5f6@git.kernel.org>
Date:   Mon, 3 Dec 2018 13:04:25 -0800
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, hpa@...or.com, ard.biesheuvel@...aro.org,
        bp@...e.de, luto@...nel.org, linux-efi@...r.kernel.org,
        pbonzini@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        riel@...riel.com, mingo@...hat.com, nstange@...e.de,
        bigeasy@...utronix.de, kvm@...r.kernel.org, Jason@...c4.com
Subject: [tip:x86/fpu] x86/fpu: Don't export __kernel_fpu_{begin,end}()

Commit-ID:  7d79adb87fa79e4a4c59424fd5b5a922861fc5f6
Gitweb:     https://git.kernel.org/tip/7d79adb87fa79e4a4c59424fd5b5a922861fc5f6
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Thu, 29 Nov 2018 16:02:10 +0100
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Mon, 3 Dec 2018 19:37:27 +0100

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

  f775b13eedee2 ("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@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Rik van Riel <riel@...riel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Nicolai Stange <nstange@...e.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kvm ML <kvm@...r.kernel.org>
Cc: linux-efi <linux-efi@...r.kernel.org>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20181129150210.2k4mawt37ow6c2vq@linutronix.de
---
 arch/x86/include/asm/efi.h     |  6 ++----
 arch/x86/include/asm/fpu/api.h | 16 ++++++----------
 arch/x86/kernel/fpu/core.c     |  6 ++----
 3 files changed, 10 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index eea40d52ca78..45864898f7e5 100644
--- 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
index a9caac9d4a72..e368d8d94ca6 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -12,17 +12,13 @@
 #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.
+ * Using the FPU in hardirq is not allowed.
  */
-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
index 2ea85b32421a..2e5003fef51a 100644
--- 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)
 {