Re: [Xen-devel] [PATCH v2 01/20] x86: make hvm_{get/set}_param accessible

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Fri, Dec 20, 2019 at 9:47 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 18.12.2019 20:40, Tamas K Lengyel wrote:
> > Currently the hvm parameters are only accessible via the HVMOP hypercalls. 
> > By
> > exposing hvm_{get/set}_param it will be possible for VM forking to copy the
> > parameters directly into the clone domain.
>
> Having peeked ahead at patch 17, where this gets used, I wonder why
> you want a pair of one-by-one functions, rather than a copy-all one.
> This then wouldn't require exposure of the functions you touch here.

Well, provided there is no such function in existence today it was
just easier to use what's already available. I still wouldn't want to
implement a one-shot function like that because this same code-path is
shared by the save-restore operations on the toolstack side, so at
least I have a reasonable assumption that it won't break on me in the
future.

> > @@ -4429,42 +4446,60 @@ static int hvmop_get_param(
> >      if ( !is_hvm_domain(d) )
> >          goto out;
> >
> > -    rc = hvm_allow_get_param(d, &a);
> > +    rc = hvm_get_param(d, a.index, &a.value);
> >      if ( rc )
> >          goto out;
> >
> > -    switch ( a.index )
> > +    rc = __copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
> > +
> > +    HVM_DBG_LOG(DBG_LEVEL_HCALL, "get param %u = %"PRIx64,
> > +                a.index, a.value);
> > +
> > + out:
> > +    rcu_unlock_domain(d);
> > +    return rc;
> > +}
> > +
> > +int hvm_get_param(
> > +    struct domain *d,
>
> If this is to be non-static, I think it would be quite nice if
> this parameter was const. This will take a prereq patch to
> constify the XSM path involved, but other than this I can't
> see anything getting in the way.

Sure.

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