[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1536959337.12990.27.camel@intel.com>
Date: Fri, 14 Sep 2018 14:08:57 -0700
From: Yu-cheng Yu <yu-cheng.yu@...el.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>
Cc: Jann Horn <jannh@...gle.com>,
the arch/x86 maintainers <x86@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
kernel list <linux-kernel@...r.kernel.org>,
linux-doc@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
linux-arch <linux-arch@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...capital.net>,
Balbir Singh <bsingharora@...il.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Florian Weimer <fweimer@...hat.com>, hjl.tools@...il.com,
Jonathan Corbet <corbet@....net>, keescook@...omium.org,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
ravi.v.shankar@...el.com, vedvyas.shanbhogue@...el.com
Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and
pmdp_set_wrprotect for _PAGE_DIRTY_SW
On Fri, 2018-09-14 at 13:46 -0700, Dave Hansen wrote:
> On 09/14/2018 01:39 PM, Yu-cheng Yu wrote:
> >
> > With the updated ptep_set_wrprotect() below, I did MADV_WILLNEED to a shadow
> > stack of 8 MB, then 10,000 fork()'s, but could not prove it is more or less
> > efficient than the other. So can we say this is probably fine in terms of
> > efficiency?
> Well, the first fork() will do all the hard work. I don't think
> subsequent fork()s will be affected.
Are you talking about a recent commit:
1b2de5d0 mm/cow: don't bother write protecting already write-protected pages
With that, subsequent fork()s will not do all the hard work.
However, I have not done that for shadow stack PTEs (do we want to do that?).
I think the additional benefit for shadow stack is small?
>
> Did you do something to ensure this code was being run?
>
> I would guess that a loop like this:
>
> for (i = 0; i < 10000; i++) {
> mprotect(addr, len, PROT_READ);
> mprotect(addr, len, PROT_READ|PROT_WRITE);
> }
>
> might show it better.
Would mprotect() do copy_one_pte()? Otherwise it will not go through
ptep_set_wrprotect()?
Powered by blists - more mailing lists