Re: [PATCH v4 2/2] xen: move TLB-flush filtering out into populate_physmap during vm creation

[Dongli Zhang <dongli.zhang@oracle.com>]

> > +    /*
> > +     * MEMF_no_tlbflush can be set only during vm creation phase when
> > +     * is_ever_unpaused is still false before this domain gets unpaused for
> > +     * the first time.
> > +     */
> > +    if ( unlikely(!d->is_ever_unpaused) )
> > +        a->memflags |= MEMF_no_tlbflush;
> 
> So you no longer mean to expose this to the caller?

hmmm.... I would prefer to expose this to the toolstack if it is OK for
maintainers.

I copy and paste Wei's comments below:

==============================================

> Rule 1. It is toolstack's responsibility to set the "MEMF_no_tlbflush" bit
> in memflags. The toolstack developers should be careful that
> "MEMF_no_tlbflush" should never be used after vm creation is finished.
> 

Is it possible to have a safety catch for this in the hypervisor? In
general IMHO we should avoid providing an interface that is possible to
create a security problem.

==============================================

Hi Wei, since it is possible to have a safety catch now in the hypervisor (the
bit is allowed only before VM creation is finished), is it OK for you to expose
MEMF_no_tlbflush bit to toolstack?

Thank you very much!

Dongli Zhang

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