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From: tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: bp@suse.de, riel@surriel.com, jgross@suse.com,
	linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
	tglx@linutronix.de, dave.hansen@intel.com, hpa@zytor.com,
	luto@kernel.org, Jason@zx2c4.com, pbonzini@redhat.com,
	mingo@kernel.org, rkrcmar@redhat.com, x86@kernel.org,
	kvm@vger.kernel.org, mingo@redhat.com
Subject: [tip:x86/fpu] x86/fpu: Only write PKRU if it is different from current
Date: Sat, 13 Apr 2019 13:55:04 -0700
Message-ID: <tip-577ff465f5a6a5a0866d75a033844810baca20a0@git.kernel.org> (raw)
In-Reply-To: <20190403164156.19645-14-bigeasy@linutronix.de>

Commit-ID:  577ff465f5a6a5a0866d75a033844810baca20a0
Gitweb:     https://git.kernel.org/tip/577ff465f5a6a5a0866d75a033844810baca20a0
Author:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Wed, 3 Apr 2019 18:41:42 +0200
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Thu, 11 Apr 2019 15:41:05 +0200

x86/fpu: Only write PKRU if it is different from current

According to Dave Hansen, WRPKRU is more expensive than RDPKRU. It has
a higher cycle cost and it's also practically a (light) speculation
barrier.

As an optimisation read the current PKRU value and only write the new
one if it is different.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-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: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: kvm ML <kvm@vger.kernel.org>
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/20190403164156.19645-14-bigeasy@linutronix.de
---
 arch/x86/include/asm/special_insns.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 34897e2b52c9..0a3c4cab39db 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -121,6 +121,13 @@ static inline void wrpkru(u32 pkru)
 
 static inline void __write_pkru(u32 pkru)
 {
+	/*
+	 * WRPKRU is relatively expensive compared to RDPKRU.
+	 * Avoid WRPKRU when it would not change the value.
+	 */
+	if (pkru == rdpkru())
+		return;
+
 	wrpkru(pkru);
 }
 

  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:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
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-bot for Sebastian Andrzej Siewior [this message]
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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