From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: "Xen-devel@lists.xensource.com" <Xen-devel@lists.xensource.com>,
Tim Deegan <tim@xen.org>, Keir Fraser <keir.xen@gmail.com>
Subject: Re: arch_set_info_guest() and cr1
Date: Thu, 22 Sep 2011 16:31:18 -0700 [thread overview]
Message-ID: <4E7BC546.9030607@goop.org> (raw)
In-Reply-To: <1316676757.23371.2.camel@zakaz.uk.xensource.com>
On 09/22/2011 12:32 AM, Ian Campbell wrote:
> (old mail, I know)
>
> On Sat, 2011-08-13 at 03:17 +0100, Jeremy Fitzhardinge wrote:
>> On 08/12/2011 03:01 PM, Mukesh Rathor wrote:
>>> Ah I see it, during save/restore, it is used.
>>> Well, I'm trying to keep the option of using PV paging with hybrid, so
>>> I may need to honor that. But that's phase 2.
>> Though it would be nice to re-enable the use of PV writable pagetables
>> to get access to HAP, and we could do without that.
>>
>> Does Xen require that the user pagetable be a proper subset of the
>> kernel pagetable? If we can assume that and get proper ring protections
>> in the HVM container, then we can simply ignore the user pagetable (and
>> would have to if we want to get good syscall performance).
> IIRC back when I did the (now completely defunct) supervisor mode kernel
> stuff that was exactly the assumption which was made and it certainly
> worked in practice (although "require" might be a strong term).
Well, I guess we could add ELF notes to allow a guest to say "I really
need separate non-intersecting user/kernel pagetables" if they really
need it. Or repurpose auto_translated_physmap to also mean "no separate
user/kernel pagetables required". Has that ever been supported for
64-bit PV guests? My memory of the chronology is that it died as a
feature at about the time that 64-bit support went in.
J
next prev parent reply other threads:[~2011-09-22 23:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-12 2:03 arch_set_info_guest() and cr1 Mukesh Rathor
2011-08-12 6:16 ` Keir Fraser
2011-08-12 22:01 ` Mukesh Rathor
2011-08-13 2:17 ` Jeremy Fitzhardinge
2011-08-15 7:35 ` Jan Beulich
2011-09-22 7:32 ` Ian Campbell
2011-09-22 23:31 ` Jeremy Fitzhardinge [this message]
2011-09-23 5:30 ` Ian Campbell
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