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Re: [Xen-devel] [PATCH V3] x86/altp2m: Hypercall to set altp2m view visibility

  • To: George Dunlap <george.dunlap@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>
  • Date: Thu, 20 Feb 2020 12:51:27 +0000
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  • Cc: Kevin Tian <kevin.tian@xxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 20 Feb 2020 12:51:32 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: AQHV5wWKuFf2vClElk6nKYx34YpPrKgkAnyAgAAIZIA=
  • Thread-topic: [PATCH V3] x86/altp2m: Hypercall to set altp2m view visibility

On 20.02.2020 14:21, George Dunlap wrote:
> On 2/19/20 9:18 AM, Alexandru Stefan ISAILA wrote:
>> At this moment a guest can call vmfunc to change the altp2m view. This
>> should be limited in order to avoid any unwanted view switch.
>> The new xc_altp2m_set_visibility() solves this by making views invisible
>> to vmfunc.
>> This is done by having a separate arch.altp2m_working_eptp that is
>> populated and made invalid in the same places as altp2m_eptp. This is
>> written to EPTP_LIST_ADDR.
>> The views are made in/visible by marking them with INVALID_MFN or
>> copying them back from altp2m_eptp.
>> To have consistency the visibility also applies to
>> p2m_switch_domain_altp2m_by_id().
> So it looks like by default the views are visible, until they're made
> non-visible?

Yes, by default all the active views are visible until they're made 

> Also, does the last line mean that the toolstack can't change to a
> "non-visible" altp2m either?

The last line means that xc_altp2m_switch_to_view() will not be able to 
switch to a non-visible view.


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