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From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Eric Biggers <ebiggers3@gmail.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rik van Riel <riel@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH 31/33] x86/fpu: Simplify and speed up fpu__copy()
Date: Sat, 23 Sep 2017 15:00:14 +0200
Message-ID: <20170923130016.21448-32-mingo@kernel.org> (raw)
In-Reply-To: <20170923130016.21448-1-mingo@kernel.org>

fpu__copy() has a preempt_disable()/enable() pair, which it had to do to
be able to atomically unlazy the current task when doing an FNSAVE.

But we don't unlazy tasks anymore, we always do direct saves/restores of
FPU context.

So remove both the unnecessary critical section, and update the comments.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/fpu/core.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4acfc0ebc160..e935f8faf287 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -206,22 +206,13 @@ int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
 	 * Save current FPU registers directly into the child
 	 * FPU context, without any memory-to-memory copying.
 	 *
-	 * We have to do all this with preemption disabled,
-	 * mostly because of the FNSAVE case, because in that
-	 * case we must not allow preemption in the window
-	 * between the FNSAVE and us marking the context lazy.
-	 *
-	 * It shouldn't be an issue as even FNSAVE is plenty
-	 * fast in terms of critical section length.
+	 * ( The function 'fails' in the FNSAVE case, which destroys
+	 *   register contents so we have to copy them back. )
 	 */
-	preempt_disable();
 	if (!copy_fpregs_to_fpstate(dst_fpu)) {
-		memcpy(&src_fpu->state, &dst_fpu->state,
-		       fpu_kernel_xstate_size);
-
+		memcpy(&src_fpu->state, &dst_fpu->state, fpu_kernel_xstate_size);
 		copy_kernel_to_fpregs(&src_fpu->state);
 	}
-	preempt_enable();
 
 	trace_x86_fpu_copy_src(src_fpu);
 	trace_x86_fpu_copy_dst(dst_fpu);
-- 
2.11.0

  parent reply index

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-23 12:59 [PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Ingo Molnar
2017-09-23 12:59 ` [PATCH 01/33] x86/fpu: Rename copyin_to_xsaves()/copyout_from_xsaves() to copy_user_to_xstate()/copy_xstate_to_user() Ingo Molnar
2017-09-26  8:21   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 02/33] x86/fpu: Split copy_xstate_to_user() into copy_xstate_to_kernel() & copy_xstate_to_user() Ingo Molnar
2017-09-26  8:22   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 03/33] x86/fpu: Remove 'ubuf' parameter from the copy_xstate_to_kernel() APIs Ingo Molnar
2017-09-26  8:22   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 04/33] x86/fpu: Remove 'kbuf' parameter from the copy_xstate_to_user() APIs Ingo Molnar
2017-09-26  8:23   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 05/33] x86/fpu: Clean up parameter order in the copy_xstate_to_*() APIs Ingo Molnar
2017-09-26  8:23   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 06/33] x86/fpu: Clean up the parameter definitions of copy_xstate_to_*() Ingo Molnar
2017-09-26  8:23   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 07/33] x86/fpu: Remove the 'start_pos' parameter from the __copy_xstate_to_*() functions Ingo Molnar
2017-09-26  8:24   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 08/33] x86/fpu: Clarify parameter names in the copy_xstate_to_*() methods Ingo Molnar
2017-09-25 19:56   ` Thomas Gleixner
2017-09-25 20:01     ` Thomas Gleixner
2017-09-26  8:24   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 09/33] x86/fpu: Change 'size_total' parameter to unsigned and standardize the size checks in copy_xstate_to_*() Ingo Molnar
2017-09-26  8:25   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 10/33] x86/fpu: Simplify __copy_xstate_to_kernel() return values Ingo Molnar
2017-09-26  8:25   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 11/33] x86/fpu: Split copy_user_to_xstate() into copy_kernel_to_xstate() & copy_user_to_xstate() Ingo Molnar
2017-09-26  8:25   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 12/33] x86/fpu: Remove 'ubuf' parameter from the copy_kernel_to_xstate() API Ingo Molnar
2017-09-26  8:26   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 13/33] x86/fpu: Remove 'kbuf' parameter from the copy_user_to_xstate() API Ingo Molnar
2017-09-26  8:26   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 14/33] x86/fpu: Flip the parameter order in copy_*_to_xstate() Ingo Molnar
2017-09-26  8:27   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 15/33] x86/fpu: Simplify fpu->fpregs_active use Ingo Molnar
2017-09-26  8:27   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 12:59 ` [PATCH 16/33] x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic Ingo Molnar
2017-09-26  8:27   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 17/33] x86/fpu: Split the state handling in fpu__drop() Ingo Molnar
2017-09-26  8:28   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 18/33] x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active Ingo Molnar
2017-09-26  8:28   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 19/33] x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active Ingo Molnar
2017-09-26  8:28   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 20/33] x86/fpu: Remove struct fpu::fpregs_active Ingo Molnar
2017-09-26  8:29   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 21/33] x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs Ingo Molnar
2017-09-26  8:29   ` [tip:x86/fpu] " tip-bot for Rik van Riel
2017-09-23 13:00 ` [PATCH 22/33] x86/fpu: Fix boolreturn.cocci warnings Ingo Molnar
2017-09-26  8:30   ` [tip:x86/fpu] " tip-bot for kbuild test robot
2017-09-23 13:00 ` [PATCH 23/33] x86/fpu: Turn WARN_ON() in context switch into WARN_ON_FPU() Ingo Molnar
2017-09-26  8:30   ` [tip:x86/fpu] " tip-bot for Andi Kleen
2017-09-23 13:00 ` [PATCH 24/33] x86/fpu: Don't let userspace set bogus xcomp_bv Ingo Molnar
2017-09-26  8:30   ` [tip:x86/fpu] " tip-bot for Eric Biggers
2017-09-23 13:00 ` [PATCH 25/33] x86/fpu: Tighten validation of user-supplied xstate_header Ingo Molnar
2017-09-23 13:00 ` [PATCH 26/33] x86/fpu: Reinitialize FPU registers if restoring FPU state fails Ingo Molnar
2017-09-26  8:31   ` [tip:x86/fpu] " tip-bot for Eric Biggers
2017-09-23 13:00 ` [PATCH 27/33] x86/fpu: Simplify fpu__activate_fpstate_read() Ingo Molnar
2017-09-26  8:31   ` [tip:x86/fpu] x86/fpu: Fix fpu__activate_fpstate_read() and update comments tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 28/33] x86/fpu: Remove fpu__current_fpstate_write_begin/end() Ingo Molnar
2017-09-26  8:32   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 29/33] x86/fpu: Rename fpu::fpstate_active to fpu::initialized Ingo Molnar
2017-09-26  8:32   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 30/33] x86/fpu: Fix stale comments about lazy FPU logic Ingo Molnar
2017-09-26  8:32   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` Ingo Molnar [this message]
2017-09-26  8:33   ` [tip:x86/fpu] x86/fpu: Simplify and speed up fpu__copy() tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 32/33] x86/fpu: Rename fpu__activate_curr() to fpu__initialize() Ingo Molnar
2017-09-26  8:33   ` [tip:x86/fpu] " tip-bot for Ingo Molnar
2017-09-23 13:00 ` [PATCH 33/33] x86/fpu: Rename fpu__activate_fpstate_read/write() to fpu__read/write() Ingo Molnar
2017-09-23 13:02 ` [PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Ingo Molnar
2017-09-23 15:03   ` Juergen Gross
2017-09-23 23:27     ` Ingo Molnar
  -- strict thread matches above, loose matches on Subject: below --
2017-09-22 17:41 [PATCH v4 0/3] x86/fpu: prevent leaking FPU registers via invalid FPU state Eric Biggers
2017-09-22 17:41 ` [PATCH v4 1/3] x86/fpu: don't let userspace set bogus xcomp_bv Eric Biggers
2017-09-22 17:41 ` [PATCH v4 2/3] x86/fpu: tighten validation of user-supplied xstate_header Eric Biggers
2017-09-22 17:41 ` [PATCH v4 3/3] x86/fpu: reinitialize FPU registers if restoring FPU state fails Eric Biggers
2017-09-23  9:09 ` [PATCH v4 0/3] x86/fpu: prevent leaking FPU registers via invalid FPU state Ingo Molnar
2017-03-29  6:26 [PATCH] x86/fpu: Turn WARN_ON in context switch into WARN_ON_FPU Andi Kleen
2017-04-24 21:00 ` [tip:perf/core] x86/fpu: Turn WARN_ON() in context switch into WARN_ON_FPU() tip-bot for Andi Kleen
2017-03-06  0:45 [tip:WIP.x86/fpu 31/31] arch/x86/kernel/fpu/xstate.c:931:9-10: WARNING: return of 0/1 in function 'xfeatures_mxcsr_quirk' with return type bool kbuild test robot
2017-03-06  0:45 ` [PATCH] x86/fpu: fix boolreturn.cocci warnings kbuild test robot
2017-03-07  7:23   ` Ingo Molnar
2017-03-07  8:33     ` Thomas Gleixner
2017-03-07  9:01       ` Ingo Molnar
2017-03-07 12:01         ` Joe Perches
2017-04-24 20:54   ` [tip:perf/core] x86/fpu: Fix " tip-bot for kbuild test robot
2017-02-09 23:43 [PATCH v2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state Rik van Riel
2017-02-10  0:02 ` Borislav Petkov
2017-02-10  0:51   ` Rik van Riel
2017-02-10  8:00     ` Ingo Molnar
2017-02-10 13:54       ` [PATCH v3] " Rik van Riel
2017-02-11 10:02         ` Ingo Molnar
2017-04-24 20:54         ` [tip:perf/core] x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs tip-bot for Rik van Riel
2017-02-10  0:45 ` [PATCH v2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state Yu-cheng Yu
2017-02-10  1:00   ` Rik van Riel
2017-02-10 17:18     ` Yu-cheng Yu

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