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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Tycho Andersen <tycho@tycho.ws>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	juerg.haefliger@hpe.com, deepa.srinivasan@oracle.com,
	Jim Mattson <jmattson@google.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	linux-mm <linux-mm@kvack.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	joao.m.martins@oracle.com, pradeep.vincent@oracle.com,
	Andi Kleen <ak@linux.intel.com>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	kanth.ghatraju@oracle.com, Liran Alon <liran.alon@oracle.com>,
	Kees Cook <keescook@google.com>,
	jsteckli@os.inf.tu-dresden.de,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	chris.hyser@oracle.com, Tyler Hicks <tyhicks@canonical.com>,
	John Haxby <john.haxby@oracle.com>, Jon Masters <jcm@redhat.com>
Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)
Date: Mon, 20 Aug 2018 16:38:31 -0700	[thread overview]
Message-ID: <CA+55aFxGpX_W_B8aiV7dWFj5=wckTSiQ4nzVx-moonO5t3e6Lw@mail.gmail.com> (raw)
In-Reply-To: <dd9657d2-f1c1-630d-4cce-7f1c67a968d6@intel.com>

On Mon, Aug 20, 2018 at 4:27 PM Dave Hansen <dave.hansen@intel.com> wrote:
>
> You're right that we could have a full physmap that we switch to for
> kmap()-like access to user pages.  But, the real problem is
> transitioning pages from kernel to user usage since it requires shooting
> down the old kernel mappings for those pages in some way.

You might decide that you simply don't care enough, and are willing to
leave possible stale TLB entries rather than shoot things down.

Then you'd still possibly see user pages in the kernel map, but only
for a fairly limited time, and only until the TLB entry gets re-used
for other reasons.

Even with kernel page table entries being marked global, their
lifetime in the TLB is likely not very long, and definitely not long
enough for some user that tries to scan for pages.

             Linus

  reply	other threads:[~2018-08-20 23:38 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-20 21:25 Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU) Konrad Rzeszutek Wilk
2018-08-20 21:48 ` Linus Torvalds
     [not found]   ` <1534801939.10027.24.camel@amazon.co.uk>
2018-08-20 22:18     ` Kees Cook
2018-08-20 22:27     ` Linus Torvalds
2018-08-20 22:35       ` Tycho Andersen
2018-08-20 22:59         ` Dave Hansen
2018-08-20 23:14           ` David Woodhouse
2018-08-20 23:26             ` Dave Hansen
2018-08-20 23:38               ` Linus Torvalds [this message]
2018-08-21  9:57       ` David Woodhouse
2018-08-21 14:01         ` Liran Alon
2018-08-21 14:22           ` David Woodhouse
2018-08-21 23:04             ` Liran Alon
2018-08-30 16:00       ` Julian Stecklina
2018-08-31 15:26         ` Tycho Andersen
2018-09-01 21:38         ` Linus Torvalds
2018-09-03 14:51           ` Julian Stecklina
2018-09-12 15:37             ` Julian Stecklina
2018-09-13  6:11               ` Juerg Haefliger
2018-09-17 10:01                 ` Julian Stecklina
2018-09-17 10:19                   ` Tycho Andersen
2018-09-17 13:27                   ` Christoph Hellwig
2018-09-14 17:06               ` Khalid Aziz
2018-09-17  9:51                 ` Julian Stecklina
2018-09-18 23:00                   ` Khalid Aziz
2018-09-24 14:45                     ` Stecklina, Julian
2018-10-15  8:07                       ` Khalid Aziz
2018-10-24 11:00                         ` Khalid Aziz
2018-10-24 15:00                           ` Tycho Andersen
2018-09-03 15:26           ` Andi Kleen
2018-09-04  9:37             ` Julian Stecklina
     [not found]           ` <CACfEFw_h5uup-anKZwfBcWMJB7gHxb9NEPTRSUAY0+t11RiQbg@mail.gmail.com>
2018-09-03 15:36             ` Andi Kleen
2018-09-07 21:30         ` Khalid Aziz
2018-08-31  8:43     ` James Bottomley
2018-09-19  1:03     ` Balbir Singh
2018-09-19 15:43       ` Jonathan Adams
2018-09-23  2:33         ` Balbir Singh
2018-09-25 14:12           ` Stecklina, Julian

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