From: Nadav Amit <namit@vmware.com>
To: Ingo Molnar <mingo@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"H . Peter Anvin " <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
<linux-kernel@vger.kernel.org>, Nadav Amit <nadav.amit@gmail.com>,
<x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
David Woodhouse <dwmw@amazon.co.uk>,
Nadav Amit <namit@vmware.com>
Subject: [RFC PATCH 1/5] x86: introduce preemption disable prefix
Date: Wed, 17 Oct 2018 17:54:16 -0700 [thread overview]
Message-ID: <20181018005420.82993-2-namit@vmware.com> (raw)
In-Reply-To: <20181018005420.82993-1-namit@vmware.com>
It is sometimes beneficial to prevent preemption for very few
instructions, or prevent preemption for some instructions that precede
a branch (this latter case will be introduced in the next patches).
To provide such functionality on x86-64, we use an empty REX-prefix
(opcode 0x40) as an indication that preemption is disabled for the
following instruction.
It is expected that this opcode is not in common use.
Signed-off-by: Nadav Amit <namit@vmware.com>
---
arch/x86/entry/entry_64.S | 10 ++++++++++
arch/x86/include/asm/nospec-branch.h | 12 ++++++++++++
2 files changed, 22 insertions(+)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index cb8a5893fd33..31d59aad496e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -643,6 +643,16 @@ retint_kernel:
jnc 1f
0: cmpl $0, PER_CPU_VAR(__preempt_count)
jnz 1f
+
+ /*
+ * Allow to use hint to prevent preemption on a certain instruction.
+ * Consider an instruction with the first byte having REX prefix
+ * without any bits set as an indication for preemption disabled.
+ */
+ movq RIP(%rsp), %rax
+ cmpb $PREEMPT_DISABLE_PREFIX, (%rax)
+ jz 1f
+
call preempt_schedule_irq
jmp 0b
1:
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 80dc14422495..0267611eb247 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -52,6 +52,12 @@
jnz 771b; \
add $(BITS_PER_LONG/8) * nr, sp;
+/*
+ * An empty REX-prefix is an indication that preemption should not take place on
+ * this instruction.
+ */
+#define PREEMPT_DISABLE_PREFIX (0x40)
+
#ifdef __ASSEMBLY__
/*
@@ -148,6 +154,12 @@
#endif
.endm
+.macro preempt_disable_prefix
+#ifdef CONFIG_PREEMPT
+ .byte PREEMPT_DISABLE_PREFIX
+#endif
+.endm
+
#else /* __ASSEMBLY__ */
#define ANNOTATE_NOSPEC_ALTERNATIVE \
--
2.17.1
next prev parent reply other threads:[~2018-10-18 0:56 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 0:54 [RFC PATCH 0/5] x86: dynamic indirect call promotion Nadav Amit
2018-10-18 0:54 ` Nadav Amit [this message]
2018-10-18 1:22 ` [RFC PATCH 1/5] x86: introduce preemption disable prefix Andy Lutomirski
2018-10-18 3:12 ` Nadav Amit
2018-10-18 3:26 ` Nadav Amit
2018-10-18 3:51 ` Andy Lutomirski
2018-10-18 16:47 ` Nadav Amit
2018-10-18 17:00 ` Andy Lutomirski
2018-10-18 17:25 ` Nadav Amit
2018-10-18 17:29 ` Andy Lutomirski
2018-10-18 17:42 ` Nadav Amit
2018-10-19 1:08 ` Nadav Amit
2018-10-19 4:29 ` Andy Lutomirski
2018-10-19 4:44 ` Nadav Amit
2018-10-20 1:22 ` Masami Hiramatsu
2018-10-19 5:00 ` Alexei Starovoitov
2018-10-19 8:22 ` Peter Zijlstra
2018-10-19 14:47 ` Alexei Starovoitov
2018-10-19 8:19 ` Peter Zijlstra
2018-10-19 10:38 ` Oleg Nesterov
2018-10-19 8:33 ` Peter Zijlstra
2018-10-19 14:29 ` Andy Lutomirski
2018-11-29 9:46 ` Peter Zijlstra
2018-10-18 7:54 ` Peter Zijlstra
2018-10-18 18:14 ` Nadav Amit
2018-10-18 0:54 ` [RFC PATCH 2/5] x86: patch indirect branch promotion Nadav Amit
2018-10-18 0:54 ` [RFC PATCH 3/5] x86: interface for accessing indirect branch locations Nadav Amit
2018-10-18 0:54 ` [RFC PATCH 4/5] x86: learning and patching indirect branch targets Nadav Amit
2018-10-18 0:54 ` [RFC PATCH 5/5] x86: relpoline: disabling interface Nadav Amit
2018-10-23 18:36 ` [RFC PATCH 0/5] x86: dynamic indirect call promotion Dave Hansen
2018-10-23 20:32 ` Nadav Amit
2018-10-23 20:37 ` Dave Hansen
2018-11-28 16:08 ` Josh Poimboeuf
2018-11-28 19:34 ` Nadav Amit
2018-11-29 0:38 ` Josh Poimboeuf
2018-11-29 1:40 ` Andy Lutomirski
2018-11-29 2:06 ` Nadav Amit
2018-11-29 3:24 ` Andy Lutomirski
2018-11-29 4:36 ` Josh Poimboeuf
2018-11-29 6:06 ` Andy Lutomirski
2018-11-29 15:19 ` Josh Poimboeuf
2018-12-01 6:52 ` Nadav Amit
2018-12-01 14:25 ` Josh Poimboeuf
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