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 19/29] x86/fpu: Only write PKRU if it is different from current
Date: Wed, 28 Nov 2018 23:20:25 +0100 [thread overview]
Message-ID: <20181128222035.2996-20-bigeasy@linutronix.de> (raw)
In-Reply-To: <20181128222035.2996-1-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)
{
--
2.20.0.rc1
next prev parent reply other threads:[~2018-11-28 22:20 UTC|newest]
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 ` [PATCH 07/29 v2] " Sebastian Andrzej Siewior
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 ` Sebastian Andrzej Siewior [this message]
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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