Re: [PATCH v14 06/11] x86/hvm/ioreq: add a new mappable resource type...

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 14 December 2017 13:46
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: Julien Grall <julien.grall@arm.com>; Andrew Cooper
> <Andrew.Cooper3@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Wei Liu
> <wei.liu2@citrix.com>; Stefano Stabellini <sstabellini@kernel.org>; xen-
> devel@lists.xenproject.org; Tim (Xen.org) <tim@xen.org>
> Subject: Re: [PATCH v14 06/11] x86/hvm/ioreq: add a new mappable
> resource type...
> 
> >>> On 14.12.17 at 10:51, <Paul.Durrant@citrix.com> wrote:
> >> From: Paul Durrant [mailto:paul.durrant@citrix.com]
> >> Sent: 28 November 2017 15:09
> >> +static int hvm_alloc_ioreq_mfn(struct hvm_ioreq_server *s, bool buf)
> >> +{
> >> +    struct domain *currd = current->domain;
> >> +    struct hvm_ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
> >> +
> >> +    if ( iorp->page )
> >> +    {
> >> +        /*
> >> +         * If a guest frame has already been mapped (which may happen
> >> +         * on demand if hvm_get_ioreq_server_info() is called), then
> >> +         * allocating a page is not permitted.
> >> +         */
> >> +        if ( !gfn_eq(iorp->gfn, INVALID_GFN) )
> >> +            return -EPERM;
> >> +
> >> +        return 0;
> >> +    }
> >> +
> >> +    /*
> >> +     * Allocated IOREQ server pages are assigned to the emulating
> >> +     * domain, not the target domain. This is because the emulator is
> >> +     * likely to be destroyed after the target domain has been torn
> >> +     * down, and we must use MEMF_no_refcount otherwise page
> allocation
> >> +     * could fail if the emulating domain has already reached its
> >> +     * maximum allocation.
> >> +     */
> >> +    iorp->page = alloc_domheap_page(currd, MEMF_no_refcount);
> >
> > This is no longer going to work as it is predicated on my original
> > modification to HYPERVISOR_mmu_update (which allowed a PV domain to
> map a
> > foreign MFN from a domain over which it had privilege as if the MFN was
> > local). Because that mechanism was decided against, this code needs to
> change
> > to use the target domain of the ioreq server rather than the calling domain.
> > I will verfy this modification and submit v15 of the series.
> >
> > Jan, are you ok for me to keep your R-b?
> 
> This is all pretty fragile - better drop it and I'll then take a look
> once you've sent the new version.

Ok. Will do.

  Paul

> 
> Jan


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