Linux-man Archive on lore.kernel.org
 help / color / Atom feed
From: Keno Fischer <keno@juliacomputing.com>
To: mtk.manpages@gmail.com
Cc: linux-man@vger.kernel.org
Subject: [PATCH] arch_prctl.2: Add ARCH_SET_CPUID subcommand
Date: Sun, 15 Mar 2020 23:21:27 -0400
Message-ID: <20200316032127.GA4619@juliacomputing.com> (raw)

This subcommand was added a few years ago to support cpuid emulation
on x86 targets, but no changes to the man page appear to have been
made at the time. This commit adds a description for it and the
corresponding getter.

Signed-off-by: Keno Fischer <keno@juliacomputing.com>
---
 man2/arch_prctl.2 | 43 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/man2/arch_prctl.2 b/man2/arch_prctl.2
index c49f4e0..e40d6bb 100644
--- a/man2/arch_prctl.2
+++ b/man2/arch_prctl.2
@@ -48,7 +48,44 @@ for the "set" operations, or as an
 .IR "unsigned long\ *" ,
 for the "get" operations.
 .PP
-Subfunctions for x86-64 are:
+Subfunctions for both x86 and x86-64 are:
+.TP
+.BR ARCH_SET_CPUID " (since Linux 4.12)"
+Enable (
+.I addr != 0
+) or disable (
+.I addr == 0
+) the
+.I cpuid
+instruction for the current thread. The instruction
+is enabled by default. If disabled,
+any execution of a
+.I cpuid
+instruction will instead generate a
+.B SIGSEGV
+signal. This feature can be used to emulate
+.I cpuid
+results that differ from what the underlying
+hardware would have produced (e.g. in a paravirtualization setting).
+This setting is preserved across
+.BR fork (2)
+and
+.BR clone (2)
+but reset to default (i.e.
+.I cpuid
+enabled) on
+.BR execve (2)
+.
+.TP
+.BR ARCH_GET_CPUID " (since Linux 4.12)"
+Return the setting of the flag manipulated by
+.B ARCH_SET_CPUID
+as the result of the system call (1 for enabled, 0 for disabled).
+.I addr
+is ignored.
+
+.TP
+Subfunctions for x86-64 only are:
 .TP
 .B ARCH_SET_FS
 Set the 64-bit base for the
@@ -96,6 +133,10 @@ is not a valid subcommand.
 .B EPERM
 .I addr
 is outside the process address space.
+.TP
+.B ENODEV
+.B ARCH_SET_CPUID
+was requested, but the underlying hardware does not support CPUID faulting.
 .\" .SH AUTHOR
 .\" Man page written by Andi Kleen.
 .SH CONFORMING TO
-- 
2.8.1


                 reply index

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

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=20200316032127.GA4619@juliacomputing.com \
    --to=keno@juliacomputing.com \
    --cc=linux-man@vger.kernel.org \
    --cc=mtk.manpages@gmail.com \
    /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

Linux-man Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-man/0 linux-man/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-man linux-man/ https://lore.kernel.org/linux-man \
		linux-man@vger.kernel.org
	public-inbox-index linux-man

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-man


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git