linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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


  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181018005420.82993-2-namit@vmware.com \
    --to=namit@vmware.com \
    --cc=bp@alien8.de \
    --cc=dwmw@amazon.co.uk \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mingo@redhat.com \
    --cc=nadav.amit@gmail.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).