Re: [Xen-devel] [PATCH v5 05/11] mm: move modify_identity_mmio to global file and drop __init

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.09.17 at 09:49, <roger.pau@xxxxxxxxxx> wrote:
> On Tue, Sep 05, 2017 at 09:01:57AM -0600, Jan Beulich wrote:
>> >>> On 14.08.17 at 16:28, <roger.pau@xxxxxxxxxx> wrote:
>> > +int modify_mmio(struct domain *d, gfn_t gfn, mfn_t mfn, unsigned long 
> nr_pages,
>> > +                bool map)
>> > +{
>> > +    int rc;
>> > +
>> > +    /*
>> > +     * ATM this function should only be used by the hardware domain
>> > +     * because it doesn't support preemption/continuation, and as such
>> > +     * can take a non-negligible amount of time. Note that it periodically
>> > +     * calls process_pending_softirqs in order to avoid stalling the 
> system.
>> > +     */
>> > +    ASSERT(is_hardware_domain(d));
>> > +
>> > +    for ( ; ; )
>> > +    {
>> > +        rc = (map ? map_mmio_regions : unmap_mmio_regions)
>> > +             (d, gfn, nr_pages, mfn);
>> > +        if ( rc == 0 )
>> > +            break;
>> > +        if ( rc < 0 )
>> > +        {
>> > +            printk(XENLOG_WARNING
>> > +                   "Failed to %smap [%" PRI_gfn ", %" PRI_gfn ") -> "
>> > +                   "[%" PRI_mfn ", %" PRI_mfn ") for d%d: %d\n",
>> > +                   map ? "" : "un", gfn_x(gfn), gfn_x(gfn_add(gfn, 
>> > nr_pages)),
>> > +                   mfn_x(mfn), mfn_x(mfn_add(mfn, nr_pages)), 
>> > d->domain_id,
>> > +                   rc);
>> > +            break;
>> > +        }
>> > +        nr_pages -= rc;
>> > +        mfn = mfn_add(mfn, rc);
>> > +        gfn = gfn_add(gfn, rc);
>> > +        process_pending_softirqs();
>> 
>> With the __init dropped, this become questionable: We shouldn't
>> do this arbitrarily; runtime use should instead force a hypercall
>> continuation (assuming that's the context it's going to be used in).
> 
> This will be used by the PCI emulation code, which is a vmexit but not
> an hypercall.
> 
> I have a plan to add continuations, but I would rather do it as part
> of using the PCI emulation for DomUs.

In which case please retain the __init while moving the function,
so there's no latent bug here in case someone else wants to
call this function in other than boot time context. The __init
should be dropped only together with making the softirq
processing here conditional, using some suitable other mechanism
post-boot.

Jan


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