From: Steven Rostedt <rostedt@goodmis.org>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Greg KH <gregkh@linuxfoundation.org>,
mingo@redhat.com, tglx@linutronix.de, xen-devel@lists.xen.org,
linux-kernel@vger.kernel.org, samu.kallio@aberdeencloud.com,
kraman@redhat.com, jwboyer@redhat.com
Subject: Re: Is: x86: mm: Fix vmalloc_fault oops during lazy MMU updates Was: Re: [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set
Date: Thu, 28 Feb 2013 13:14:11 -0500 [thread overview]
Message-ID: <20130228181411.GD9161@home.goodmis.org> (raw)
In-Reply-To: <512F856B.5090801@oracle.com>
On Thu, Feb 28, 2013 at 11:27:23AM -0500, Boris Ostrovsky wrote:
> On 02/28/2013 11:22 AM, Borislav Petkov wrote:
> >On Thu, Feb 28, 2013 at 11:20:20AM -0500, Boris Ostrovsky wrote:
> >>On 02/28/2013 11:10 AM, Borislav Petkov wrote:
> >>>On Thu, Feb 28, 2013 at 07:53:44AM -0800, H. Peter Anvin wrote:
> >>>>At the very least we should have an early filter for the **COMMON!**
> >>>>case that we are not on a PV platform.
> >>>... or, patch it out with the alternatives on baremetal, as Steven
> >>>suggested.
>
> What was the suggestion exactly? I don't remember seeing that message.
Yeah, Borislav talked to me privately on IRC about this and I pointed
him to the apply_paravirt() function in arch/x86/kernel/alternative.c
where things that apply only to paravirt get patched out on baremetal.
It may add complexity, but there's a method for doing it and I rather
not burden baremetal for pravirt nonsense. I know adding a simple call
to preempt_count() can show a noticable impact to function tracing. It
requires referencing the gs segment register and doing some offset
games (as it's stored as a per cpu pointer) to find the stack.
I was actually a bit amazed that it had as big of an impact as it did. I
can understand why Christoph Lameter tried hard not to add a
preempt_disable() in his code for just a tiny location.
-- Steve
>
> -boris
>
> >>>
> >>I think making a check for paravirt_enabled() is safe enough. I'll
> >>send a patch shortly.
> >Why not make it absolutely for free?
> >
prev parent reply other threads:[~2013-02-28 18:14 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-26 23:57 [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set Boris Ostrovsky
2013-02-27 22:40 ` H. Peter Anvin
2013-02-27 23:00 ` Greg KH
2013-02-27 23:07 ` H. Peter Anvin
2013-02-28 14:29 ` Is: x86: mm: Fix vmalloc_fault oops during lazy MMU updates Was: " Konrad Rzeszutek Wilk
2013-02-28 15:38 ` Borislav Petkov
2013-02-28 15:53 ` H. Peter Anvin
2013-02-28 16:10 ` Borislav Petkov
2013-02-28 16:20 ` Boris Ostrovsky
2013-02-28 16:22 ` Borislav Petkov
2013-02-28 16:24 ` H. Peter Anvin
2013-02-28 16:27 ` Boris Ostrovsky
2013-02-28 16:32 ` Borislav Petkov
2013-02-28 18:14 ` Steven Rostedt [this message]
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