From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: 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>,
"Rik van Riel" <riel@surriel.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>
Subject: [PATCH 12/22] x86/fpu: Only write PKRU if it is different from current
Date: Wed, 9 Jan 2019 12:47:34 +0100 [thread overview]
Message-ID: <20190109114744.10936-13-bigeasy@linutronix.de> (raw)
In-Reply-To: <20190109114744.10936-1-bigeasy@linutronix.de>
Dave Hansen says that the `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>
---
arch/x86/include/asm/special_insns.h | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 43c029cdc3fe8..c2ccf71b22dd6 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -107,7 +107,7 @@ static inline u32 __read_pkru(void)
return pkru;
}
-static inline void __write_pkru(u32 pkru)
+static inline void __write_pkru_insn(u32 pkru)
{
u32 ecx = 0, edx = 0;
@@ -118,6 +118,17 @@ static inline void __write_pkru(u32 pkru)
asm volatile(".byte 0x0f,0x01,0xef\n\t"
: : "a" (pkru), "c"(ecx), "d"(edx));
}
+
+static inline void __write_pkru(u32 pkru)
+{
+ /*
+ * Writting PKRU is expensive. Only write the PKRU value if it is
+ * different from the current one.
+ */
+ if (pkru == __read_pkru())
+ return;
+ __write_pkru_insn(pkru);
+}
#else
static inline u32 __read_pkru(void)
{
--
2.20.1
next prev parent reply other threads:[~2019-01-09 11:50 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 11:47 [PATCH v6] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 01/22] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-01-14 16:24 ` Borislav Petkov
2019-02-05 10:08 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 02/22] x86/fpu: Remove fpu__restore() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 03/22] x86/fpu: Remove preempt_disable() in fpu__clear() Sebastian Andrzej Siewior
2019-01-14 18:55 ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 04/22] x86/fpu: Always init the `state' " Sebastian Andrzej Siewior
2019-01-14 19:32 ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-01-16 19:36 ` Borislav Petkov
2019-01-16 22:40 ` Sebastian Andrzej Siewior
2019-01-17 12:22 ` Borislav Petkov
2019-01-18 21:14 ` Sebastian Andrzej Siewior
2019-01-18 21:17 ` Dave Hansen
2019-01-18 21:37 ` Sebastian Andrzej Siewior
2019-01-18 21:43 ` Dave Hansen
2019-01-21 11:21 ` Oleg Nesterov
2019-01-22 13:40 ` Borislav Petkov
2019-01-22 16:15 ` Oleg Nesterov
2019-01-22 17:00 ` Borislav Petkov
2019-02-05 11:34 ` Sebastian Andrzej Siewior
2019-02-05 11:17 ` Sebastian Andrzej Siewior
2019-02-26 16:38 ` Oleg Nesterov
2019-03-08 18:12 ` Sebastian Andrzej Siewior
2019-02-05 14:37 ` [PATCH 05/22 v2] " Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 06/22] x86/fpu: Don't save fxregs for ia32 frames " Sebastian Andrzej Siewior
2019-01-24 11:17 ` Borislav Petkov
2019-02-05 16:43 ` [PATCH 06/22 v2] x86/fpu: Don't save fxregs for ia32 frames in Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 07/22] x86/fpu: Remove fpu->initialized Sebastian Andrzej Siewior
2019-01-24 13:34 ` Borislav Petkov
2019-02-05 18:03 ` Sebastian Andrzej Siewior
2019-02-06 14:01 ` Borislav Petkov
2019-02-07 10:13 ` Sebastian Andrzej Siewior
2019-02-07 10:37 ` Borislav Petkov
2019-02-05 18:06 ` [PATCH 07/22 v2] " Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 08/22] x86/fpu: Remove user_fpu_begin() Sebastian Andrzej Siewior
2019-01-25 15:18 ` Borislav Petkov
2019-02-05 18:16 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 09/22] x86/fpu: Add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2019-01-28 18:23 ` Borislav Petkov
2019-02-07 10:43 ` Sebastian Andrzej Siewior
2019-02-13 9:30 ` Borislav Petkov
2019-02-14 14:51 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 10/22] x86/fpu: Make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2019-01-28 18:30 ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 11/22] x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() " Sebastian Andrzej Siewior
2019-01-28 18:49 ` Borislav Petkov
2019-02-07 11:13 ` Sebastian Andrzej Siewior
2019-02-13 9:31 ` Borislav Petkov
2019-01-09 11:47 ` Sebastian Andrzej Siewior [this message]
2019-01-23 18:09 ` [PATCH 12/22] x86/fpu: Only write PKRU if it is different from current Dave Hansen
2019-02-07 11:27 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 13/22] x86/pkeys: Don't check if PKRU is zero before writting it Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 14/22] x86/fpu: Eager switch PKRU state Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 15/22] x86/entry: Add TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-01-30 11:55 ` Borislav Petkov
2019-02-07 11:49 ` Sebastian Andrzej Siewior
2019-02-13 9:35 ` Borislav Petkov
2019-02-14 15:28 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 16/22] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2019-01-30 11:43 ` Borislav Petkov
2019-02-07 13:28 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 17/22] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2019-01-30 11:56 ` Borislav Petkov
2019-01-30 12:28 ` Sebastian Andrzej Siewior
2019-01-30 12:53 ` Borislav Petkov
2019-02-07 14:10 ` Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 18/22] x86/fpu: Update xstate's PKRU value on write_pkru() Sebastian Andrzej Siewior
2019-01-23 17:28 ` Dave Hansen
2019-01-09 11:47 ` [PATCH 19/22] x86/fpu: Inline copy_user_to_fpregs_zeroing() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 20/22] x86/fpu: Let __fpu__restore_sig() restore the !32bit+fxsr frame from kernel memory Sebastian Andrzej Siewior
2019-01-30 21:29 ` Borislav Petkov
2019-01-09 11:47 ` [PATCH 21/22] x86/fpu: Merge the two code paths in __fpu__restore_sig() Sebastian Andrzej Siewior
2019-01-09 11:47 ` [PATCH 22/22] x86/fpu: Defer FPU state load until return to userspace Sebastian Andrzej Siewior
2019-01-31 9:16 ` Borislav Petkov
2019-01-15 12:44 ` [PATCH v6] x86: load FPU registers on return to userland David Laight
2019-01-15 13:15 ` 'Sebastian Andrzej Siewior'
2019-01-15 14:33 ` David Laight
2019-01-15 19:46 ` Dave Hansen
2019-01-15 20:26 ` Andy Lutomirski
2019-01-15 20:54 ` Dave Hansen
2019-01-15 21:11 ` Andy Lutomirski
2019-01-16 10:31 ` David Laight
2019-01-16 10:18 ` David Laight
2019-01-30 11:35 ` Borislav Petkov
2019-01-30 12:06 ` Sebastian Andrzej Siewior
2019-01-30 12:27 ` Borislav Petkov
2019-02-08 13:12 ` Sebastian Andrzej Siewior
2019-02-13 15:54 ` Sebastian Andrzej Siewior
2019-02-21 11:49 [PATCH v7] " Sebastian Andrzej Siewior
2019-02-21 11:50 ` [PATCH 12/22] x86/fpu: Only write PKRU if it is different from current Sebastian Andrzej Siewior
2019-02-25 18:08 ` Dave Hansen
2019-03-08 17:24 ` Sebastian Andrzej Siewior
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