Re: [PATCH 3/4] xen/arm, libxl: Revert XEN_DOMCTL_shadow_op; use p2m mempool hypercalls

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 16 Nov 2022, Andrew Cooper wrote:
> On 16/11/2022 01:37, Stefano Stabellini wrote:
> > On Wed, 26 Oct 2022, Andrew Cooper wrote:
> >> This reverts most of commit cf2a68d2ffbc3ce95e01449d46180bddb10d24a0, and 
> >> bits
> >> of cbea5a1149ca7fd4b7cdbfa3ec2e4f109b601ff7.
> >>
> >> First of all, with ARM borrowing x86's implementation, the logic to set the
> >> pool size should have been common, not duplicated.  Introduce
> >> libxl__domain_set_p2m_pool_size() as a shared implementation, and use it 
> >> from
> >> the ARM and x86 paths.  It is left as an exercise to the reader to judge 
> >> how
> >> libxl/xl can reasonably function without the ability to query the pool 
> >> size...
> >>
> >> Remove ARM's p2m_domctl() infrastructure now the functioanlity has been
> >> replaced with a working and unit tested interface.
> >>
> >> This is part of XSA-409 / CVE-2022-33747.
> > Genuine question: I can see this patch removes the implementation of
> > XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION on ARM. It also switches libxl (both
> > ARM and x86) to the new hypercall.
> >
> > Why keep the old hypercall (XEN_DOMCTL_shadow_op and
> > XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION) implementation on x86 (not on ARM)?
> >
> > Is that because it was only recently implemented? And not actually
> > present in any past Xen release?
> >
> > If so, please add a note about this in the commit message. Also, if that
> > is the case, I think this patch series should go in 4.17. If it is too
> > late to get it in before the release, then we should backport it to 4.17
> > as soon as possible. That's because ideally we want to keep the
> > hypercall interface changes down to a minimum.
> 
> On ARM, the hypercall has existed for a little over 4 weeks, and isn't
> in any released version of Xen (yet).
> 
> On x86, the hypercall has existed for more than a decade, and has known
> out-of-tree users.  It needs to be deprecated properly, which in this
> case means "phased out in the 4.18 cycle once known callers have been
> adapted to the new hypercall".

Understoon. Then I am in favor of getting all 4 patches in 4.17, either
before the release or via backports.