Re: [Xen-devel] arch_set_info_guest() and cr1

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel