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Re: [PATCH V7] x86/altp2m: Hypercall to set altp2m view visibility

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Isaila Alexandru <aisaila@xxxxxxxxxxxxxxx>
  • Date: Tue, 31 Mar 2020 10:54:41 +0300
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  • Cc: Kevin Tian <kevin.tian@xxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, 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>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 31 Mar 2020 07:54:48 +0000
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On 31.03.2020 10:43, Jan Beulich wrote:
On 30.03.2020 08:54, Alexandru 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

The usage of this hypercall is aimed at dom0 having a logic with a number of 
created and at some time there is a need to be sure that only some of the views
can be switched, saving the rest and making them visible when the time
is right.

Note: If altp2m mode is set to mixed the guest is able to change the view
visibility and then call vmfunc.

Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>

For v6 I did provide a hypervisor side R-b; I didn't think ...

No you didn't.

Changes since V6:
        - Update commit message.

... this alone would have warranted to drop it?

I don't think so and if you provide a r-b now I will add it if it will be a need for another version (if nothing big changes).




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