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From: tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, bp@suse.de,
	nstange@suse.de, Jason@zx2c4.com, x86@kernel.org,
	riel@surriel.com, pbonzini@redhat.com, jannh@google.com,
	luto@kernel.org, dave.hansen@intel.com, mingo@redhat.com,
	bigeasy@linutronix.de, hpa@zytor.com, aubrey.li@intel.com,
	tglx@linutronix.de, rkrcmar@redhat.com, kvm@vger.kernel.org
Subject: [tip:x86/fpu] x86/fpu: Remove user_fpu_begin()
Date: Sat, 13 Apr 2019 13:51:29 -0700
Message-ID: <tip-0169f53e0d97bb675075506810494bd86b8c934e@git.kernel.org> (raw)
In-Reply-To: <20190403164156.19645-9-bigeasy@linutronix.de>

Commit-ID:  0169f53e0d97bb675075506810494bd86b8c934e
Gitweb:     https://git.kernel.org/tip/0169f53e0d97bb675075506810494bd86b8c934e
Author:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Wed, 3 Apr 2019 18:41:37 +0200
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Wed, 10 Apr 2019 15:58:44 +0200

x86/fpu: Remove user_fpu_begin()

user_fpu_begin() sets fpu_fpregs_owner_ctx to task's fpu struct. This is
always the case since there is no lazy FPU anymore.

fpu_fpregs_owner_ctx is used during context switch to decide if it needs
to load the saved registers or if the currently loaded registers are
valid. It could be skipped during a

  taskA -> kernel thread -> taskA

switch because the switch to the kernel thread would not alter the CPU's
sFPU tate.

Since this field is always updated during context switch and
never invalidated, setting it manually (in user context) makes no
difference. A kernel thread with kernel_fpu_begin() block could
set fpu_fpregs_owner_ctx to NULL but a kernel thread does not use
user_fpu_begin().

This is a leftover from the lazy-FPU time.

Remove user_fpu_begin(), it does not change fpu_fpregs_owner_ctx's
content.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aubrey Li <aubrey.li@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-9-bigeasy@linutronix.de
---
 arch/x86/include/asm/fpu/internal.h | 17 -----------------
 arch/x86/kernel/fpu/core.c          |  4 +---
 arch/x86/kernel/fpu/signal.c        |  1 -
 3 files changed, 1 insertion(+), 21 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 04042eacc852..54f70cae2f15 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -532,23 +532,6 @@ static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu)
 	}
 }
 
-/*
- * Needs to be preemption-safe.
- *
- * NOTE! user_fpu_begin() must be used only immediately before restoring
- * the save state. It does not do any saving/restoring on its own. In
- * lazy FPU mode, it is just an optimization to avoid a #NM exception,
- * the task can lose the FPU right after preempt_enable().
- */
-static inline void user_fpu_begin(void)
-{
-	struct fpu *fpu = &current->thread.fpu;
-
-	preempt_disable();
-	fpregs_activate(fpu);
-	preempt_enable();
-}
-
 /*
  * MXCSR and XCR definitions:
  */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 97e27de2b7c0..739ca3ae2bdc 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -335,10 +335,8 @@ void fpu__clear(struct fpu *fpu)
 	 * Make sure fpstate is cleared and initialized.
 	 */
 	fpu__initialize(fpu);
-	if (static_cpu_has(X86_FEATURE_FPU)) {
-		user_fpu_begin();
+	if (static_cpu_has(X86_FEATURE_FPU))
 		copy_init_fpstate_to_fpregs();
-	}
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 34989d2a8893..155f4552413e 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -322,7 +322,6 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		 * For 64-bit frames and 32-bit fsave frames, restore the user
 		 * state to the registers directly (with exceptions handled).
 		 */
-		user_fpu_begin();
 		if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
 			fpu__clear(fpu);
 			return -1;

  reply index

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-03 16:41 [PATCH v9 00/27] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 01/27] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-04-13 20:46   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 02/27] x86/fpu: Remove fpu__restore() Sebastian Andrzej Siewior
2019-04-13 20:47   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 03/27] x86/fpu: Remove preempt_disable() in fpu__clear() Sebastian Andrzej Siewior
2019-04-13 20:48   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 04/27] x86/fpu: Always init the `state' " Sebastian Andrzej Siewior
2019-04-13 20:48   ` [tip:x86/fpu] x86/fpu: Always init the state " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 05/27] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-04-13 20:49   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 06/27] x86/fpu: Don't save fxregs for ia32 frames " Sebastian Andrzej Siewior
2019-04-13 20:50   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 07/27] x86/fpu: Remove fpu->initialized Sebastian Andrzej Siewior
2019-04-13 20:50   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 08/27] x86/fpu: Remove user_fpu_begin() Sebastian Andrzej Siewior
2019-04-13 20:51   ` tip-bot for Sebastian Andrzej Siewior [this message]
2019-04-03 16:41 ` [PATCH 09/27] x86/fpu: Add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2019-04-13 20:52   ` [tip:x86/fpu] x86/fpu: Add an __fpregs_load_activate() internal helper tip-bot for Rik van Riel
2019-04-03 16:41 ` [PATCH 10/27] x86/fpu: Make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2019-04-13 20:52   ` [tip:x86/fpu] x86/fpu: Make __raw_xsave_addr() use a " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 11/27] x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() use " Sebastian Andrzej Siewior
2019-04-13 20:53   ` [tip:x86/fpu] x86/fpu: Use a feature number instead of mask in two more helpers tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 12/27] x86/pkru: Provide .*_pkru_ins() functions Sebastian Andrzej Siewior
2019-04-10 16:36   ` Borislav Petkov
2019-04-10 16:52     ` Borislav Petkov
2019-04-10 21:25       ` Sebastian Andrzej Siewior
2019-04-10 21:29         ` Dave Hansen
2019-04-11 13:24           ` Borislav Petkov
2019-04-13 20:54   ` [tip:x86/fpu] x86/pkeys: Provide *pkru() helpers tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 13/27] x86/fpu: Only write PKRU if it is different from current Sebastian Andrzej Siewior
2019-04-13 20:55   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 14/27] x86/pkeys: Don't check if PKRU is zero before writting it Sebastian Andrzej Siewior
2019-04-13 20:55   ` [tip:x86/fpu] x86/pkeys: Don't check if PKRU is zero before writing it tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 15/27] x86/fpu: Eager switch PKRU state Sebastian Andrzej Siewior
2019-04-13 20:56   ` [tip:x86/fpu] " tip-bot for Rik van Riel
2019-04-03 16:41 ` [PATCH 16/27] x86/entry: Add TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-04-13 20:57   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 17/27] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-04-13 20:57   ` [tip:x86/fpu] " tip-bot for Rik van Riel
2019-04-03 16:41 ` [PATCH 18/27] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-04-13 20:58   ` [tip:x86/fpu] " tip-bot for Rik van Riel
2019-04-03 16:41 ` [PATCH 19/27] x86/fpu: Update xstate's PKRU value on write_pkru() Sebastian Andrzej Siewior
2019-04-08 18:14   ` Dave Hansen
2019-04-08 20:03     ` Sebastian Andrzej Siewior
2019-04-13 20:59   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 20/27] x86/fpu: Inline copy_user_to_fpregs_zeroing() Sebastian Andrzej Siewior
2019-04-13 21:00   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 21/27] x86/fpu: Let __fpu__restore_sig() restore the !32bit+fxsr frame from kernel memory Sebastian Andrzej Siewior
2019-04-13 21:00   ` [tip:x86/fpu] x86/fpu: Restore from kernel memory on the 64-bit path too tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 22/27] x86/fpu: Merge the two code paths in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-04-13 21:01   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 23/27] x86/fpu: Defer FPU state load until return to userspace Sebastian Andrzej Siewior
2019-04-12 14:36   ` Borislav Petkov
2019-04-12 15:24     ` Sebastian Andrzej Siewior
2019-04-12 16:22       ` Borislav Petkov
2019-04-12 16:37         ` Sebastian Andrzej Siewior
2019-04-12 16:48           ` Borislav Petkov
2019-04-12 17:19             ` Sebastian Andrzej Siewior
2019-04-12 17:29               ` Borislav Petkov
2019-04-15  9:14                 ` Sebastian Andrzej Siewior
2019-04-13 21:02   ` [tip:x86/fpu] " tip-bot for Rik van Riel
2019-04-03 16:41 ` [PATCH 24/27] x86/fpu: Add a fastpath to __fpu__restore_sig() Sebastian Andrzej Siewior
2019-04-08 17:05   ` Thomas Gleixner
2019-04-08 20:02     ` Sebastian Andrzej Siewior
2019-04-09  7:27       ` Thomas Gleixner
2019-04-12 17:17   ` Borislav Petkov
2019-04-12 17:27     ` Sebastian Andrzej Siewior
2019-04-13 21:02   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 25/27] x86/fpu: Add a fastpath to copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-04-13 21:03   ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 26/27] x86/fpu: Restore FPU register in copy_fpstate_to_sigframe() in order to use the fastpath Sebastian Andrzej Siewior
2019-04-13 21:04   ` [tip:x86/fpu] x86/fpu: Restore regs " tip-bot for Sebastian Andrzej Siewior
2019-04-03 16:41 ` [PATCH 27/27] x86/pkeys: add PKRU value to init_fpstate Sebastian Andrzej Siewior
2019-04-13 21:05   ` [tip:x86/fpu] x86/pkeys: Add " tip-bot for Sebastian Andrzej Siewior
2019-04-04 14:01 ` [PATCH v9 00/27] x86: load FPU registers on return to userland David Laight
2019-04-04 14:14   ` 'Sebastian Andrzej Siewior'
2019-04-04 14:26     ` Andy Lutomirski
2019-04-04 14:31       ` Sebastian Andrzej Siewior
2019-04-04 15:10       ` David Laight
2019-04-08 17:08 ` Thomas Gleixner
2019-04-12 18:30 ` Borislav Petkov
2019-04-15  8:58   ` Sebastian Andrzej Siewior

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