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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rik van Riel <riel@surriel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	"Andy Lutomirski" <luto@kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
	"Dave Hansen" <dave.hansen@linux.intel.com>
Subject: [PATCH 07/29 v2] x86/fpu: don't export __kernel_fpu_{begin|end}()
Date: Thu, 29 Nov 2018 16:02:10 +0100
Message-ID: <20181129150210.2k4mawt37ow6c2vq@linutronix.de> (raw)
In-Reply-To: <da61c2af8aab3348d6fb09889b5531bec7e2f842.camel@surriel.com>

There is one user using __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}(), it can be
made static and not exported anymore.

Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
v1…v2: `carefull' -> `careful'

 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 eea40d52ca785..45864898f7e50 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 a9caac9d4a729..e368d8d94ca68 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 2ea85b32421a0..2e5003fef51a9 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)
 {
-- 
2.20.0.rc1

  reply index

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-28 22:20 [PATCH v5] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 01/29] x86/fpu: Use ULL for shift in xfeature_uncompacted_offset() Sebastian Andrzej Siewior
2018-11-29  1:52   ` Rik van Riel
2018-12-03 21:00   ` [tip:x86/fpu] x86/fpu: Use unsigned long long " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 02/29] x86/entry/32: Remove asm/math_emu.h include Sebastian Andrzej Siewior
2018-11-29  1:52   ` Rik van Riel
2018-12-03 21:01   ` [tip:x86/fpu] x86/process/32: " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 03/29] x86/entry: Remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-11-29  1:53   ` Rik van Riel
2018-12-03 21:02   ` [tip:x86/fpu] x86/thread_info: " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 04/29] x86/pkeys: Make init_pkru_value static Sebastian Andrzej Siewior
2018-11-29  1:53   ` Rik van Riel
2018-12-03 21:02   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 05/29] x86/fpu: add might_fault() to user_insn() Sebastian Andrzej Siewior
2018-11-29  1:54   ` Rik van Riel
2018-12-03 21:03   ` [tip:x86/fpu] x86/fpu: Add " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 06/29] x86/fpu: Update comment for __raw_xsave_addr() Sebastian Andrzej Siewior
2018-11-29  1:56   ` Rik van Riel
2018-12-03 21:03   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 07/29] x86/fpu: don't export __kernel_fpu_{begin|end}() Sebastian Andrzej Siewior
2018-11-29  2:00   ` Rik van Riel
2018-11-29 15:02     ` Sebastian Andrzej Siewior [this message]
2018-12-03 21:04       ` [tip:x86/fpu] x86/fpu: Don't export __kernel_fpu_{begin,end}() tip-bot for Sebastian Andrzej Siewior
2018-12-03 21:12         ` Ard Biesheuvel
2018-12-03 22:08           ` Borislav Petkov
2018-12-04 11:39             ` Borislav Petkov
2018-12-04 12:15             ` Sebastian Andrzej Siewior
2018-12-04 12:33               ` Borislav Petkov
2018-12-04 11:45       ` tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 08/29] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Sebastian Andrzej Siewior
2018-12-06 20:07   ` Borislav Petkov
2018-12-07  8:17     ` Sebastian Andrzej Siewior
2018-12-07 10:19       ` Borislav Petkov
2018-11-28 22:20 ` [PATCH 09/29] x86/fpu: Remove fpu__restore() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 10/29] x86/fpu: Remove preempt_disable() in fpu__clear() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 11/29] x86/fpu: Always init the `state' " Sebastian Andrzej Siewior
2018-12-12 17:11   ` Borislav Petkov
2018-12-13 14:35     ` Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 12/29] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 13/29] x86/fpu: Don't save fxregs for ia32 frames " Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 14/29] x86/fpu: Remove fpu->initialized Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 15/29] x86/fpu: Remove user_fpu_begin() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 16/29] x86/fpu: Add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 17/29] x86/fpu: Make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 18/29] x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() " Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 19/29] x86/fpu: Only write PKRU if it is different from current Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 20/29] x86/pkeys: Don't check if PKRU is zero before writting it Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 21/29] x86/fpu: Eager switch PKRU state Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 22/29] x86/entry: Add TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 23/29] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 24/29] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 25/29] x86/fpu: Update xstate's PKRU value on write_pkru() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 26/29] x86/fpu: Inline copy_user_to_fpregs_zeroing() Sebastian Andrzej Siewior
2018-11-28 23:09   ` Joey Pabalinas
2018-11-28 22:20 ` [PATCH 27/29] x86/fpu: Let __fpu__restore_sig() restore the !32bit+fxsr frame from kernel memory Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 28/29] x86/fpu: Merge the two code paths in __fpu__restore_sig() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 29/29] x86/fpu: Defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-11-29 15:00   ` Sebastian Andrzej Siewior
2018-12-10 14:41   ` Sebastian Andrzej Siewior
2018-11-30 11:52 ` [PATCH v5] x86: load FPU registers on return to userland Sebastian Andrzej Siewior

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