From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
a.p.zijlstra@chello.nl, stable@kernel.org, tglx@linutronix.de,
mingo@elte.hu, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case
Date: Mon, 20 Feb 2012 13:26:12 -0500 [thread overview]
Message-ID: <1329762372.25686.35.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <CA+55aFxfAn9MWRgS3O5k2tqN5ys1XrhSFVO5_9ZAoZKDVgNfGA@mail.gmail.com>
On Mon, 2012-02-20 at 10:03 -0800, Linus Torvalds wrote:
> On Mon, Feb 20, 2012 at 3:47 AM, tip-bot for Steven Rostedt
> <rostedt@goodmis.org> wrote:
> > /*
> > + * If %cs was not the kernel segment, then the NMI triggered in user
> > + * space, which means it is definitely not nested.
> > + */
> > + cmp $__KERNEL_CS, 16(%rsp)
> > + jne first_nmi
>
> I don't like how you wrote 'cmp' without a size, especially with none
> of the arguments then giving a size either. Usually there's a register
> name or something that gives you the size, but not here.
>
> I guess there is some default size that gas will use, but at least
> some versions of gas have traditionally errored out instead of
> guessing on sizes. Maybe x86-64 doesn't use those gas versions any
> more, but still..
OK, I'll send an update fix to use cmpq.
>From HPA's email:
"User space can change %cs, but it can never set it to __KERNEL_CS;
specifically user space can never set the bottom two bits in CS to
zero."
I'm not sure it matters, but I'll change it anyway since we are
comparing an 8 byte word on the stack.
-- Steve
next prev parent reply other threads:[~2012-02-20 18:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-19 2:06 [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determine nested NMI Steven Rostedt
2012-02-19 12:56 ` Ingo Molnar
2012-02-19 13:46 ` hpanvin@gmail.com
2012-02-19 13:48 ` Ingo Molnar
2012-02-19 20:34 ` Steven Rostedt
2012-02-19 20:45 ` H. Peter Anvin
2012-02-19 21:00 ` Steven Rostedt
2012-02-19 14:57 ` Steven Rostedt
2012-02-20 8:10 ` Ingo Molnar
2012-02-20 14:41 ` Steven Rostedt
2012-02-20 15:34 ` Ingo Molnar
2012-02-20 17:07 ` H. Peter Anvin
2012-02-19 21:43 ` [PATCH v2][GIT PULL][v3.3] x86: Test saved %cs " Steven Rostedt
2012-02-20 11:47 ` [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case tip-bot for Steven Rostedt
2012-02-20 16:51 ` Steven Rostedt
2012-02-27 21:29 ` Greg KH
2012-02-20 18:03 ` Linus Torvalds
2012-02-20 18:26 ` Steven Rostedt [this message]
2012-02-21 22:08 ` [tip:x86/urgent] x86: Specify a size for the cmp in the NMI handler tip-bot for Steven Rostedt
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