RE: [PATCH v8 6/8] common/domain: add a domain context record for shared_info...

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 16 September 2020 15:43
> To: Paul Durrant <paul@xxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Durrant, Paul <pdurrant@xxxxxxxxxxxx>; 
> Ian Jackson
> <ian.jackson@xxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper 
> <andrew.cooper3@xxxxxxxxxx>; George
> Dunlap <george.dunlap@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Stefano 
> Stabellini
> <sstabellini@xxxxxxxxxx>
> Subject: RE: [EXTERNAL] [PATCH v8 6/8] common/domain: add a domain context 
> record for shared_info...
> 
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> 
> 
> On 15.09.2020 18:17, Paul Durrant wrote:
> > +static int load_shared_info(struct domain *d, struct domain_context *c)
> > +{
> > +    struct domain_shared_info_context ctxt;
> > +    size_t hdr_size = offsetof(typeof(ctxt), buffer);
> > +    unsigned int i;
> > +    int rc;
> > +
> > +    rc = DOMAIN_LOAD_BEGIN(SHARED_INFO, c, &i);
> > +    if ( rc )
> > +        return rc;
> > +
> > +    if ( i ) /* expect only a single instance */
> > +        return -ENXIO;
> > +
> > +    rc = domain_load_data(c, &ctxt, hdr_size);
> > +    if ( rc )
> > +        return rc;
> > +
> > +    if ( ctxt.buffer_size > sizeof(shared_info_t) ||
> > +         (ctxt.flags & ~DOMAIN_SAVE_32BIT_SHINFO) )
> > +        return -EINVAL;
> > +
> > +    if ( ctxt.flags & DOMAIN_SAVE_32BIT_SHINFO )
> > +    {
> > +#ifdef CONFIG_COMPAT
> > +        has_32bit_shinfo(d) = true;
> > +#else
> > +        return -EINVAL;
> > +#endif
> > +    }
> > +
> > +    if ( is_pv_domain(d) )
> > +    {
> > +        shared_info_t *shinfo = xmalloc(shared_info_t);
> > +
> > +        rc = domain_load_data(c, shinfo, sizeof(*shinfo));
> 
> You need to check the allocation's success first.

Oops, yes.

> But of course the
> question is why you don't read directly into d->shared_info. The
> domain is paused at this point, isn't it?
> 

It is, but domain_create() may have initialized something outside of the areas 
we want to touch; I'm trying to follow what the existing restore code in 
toolstack currently does.

> > +        if ( rc )
> > +        {
> > +            xfree(shinfo);
> > +            return rc;
> > +        }
> > +
> > +#ifdef CONFIG_COMPAT
> > +        if ( has_32bit_shinfo(d) )
> > +        {
> > +            memcpy(&d->shared_info->compat.vcpu_info,
> > +                   &shinfo->compat.vcpu_info,
> > +                   sizeof(d->shared_info->compat.vcpu_info));
> > +            memcpy(&d->shared_info->compat.arch,
> > +                   &shinfo->compat.arch,
> > +                   sizeof(d->shared_info->compat.vcpu_info));
> > +            memset(&d->shared_info->compat.evtchn_pending,
> > +                   0,
> > +                   sizeof(d->shared_info->compat.evtchn_pending));
> > +            memset(&d->shared_info->compat.evtchn_mask,
> > +                   0xff,
> > +                   sizeof(d->shared_info->compat.evtchn_mask));
> > +
> > +            d->shared_info->compat.arch.pfn_to_mfn_frame_list_list = 0;
> > +            for ( i = 0; i < XEN_LEGACY_MAX_VCPUS; i++ )
> > +                d->shared_info->compat.vcpu_info[i].evtchn_pending_sel = 0;
> > +        }
> > +        else
> > +        {
> > +            memcpy(&d->shared_info->native.vcpu_info,
> > +                   &shinfo->native.vcpu_info,
> > +                   sizeof(d->shared_info->native.vcpu_info));
> > +            memcpy(&d->shared_info->native.arch,
> > +                   &shinfo->native.arch,
> > +                   sizeof(d->shared_info->native.arch));
> > +            memset(&d->shared_info->native.evtchn_pending,
> > +                   0,
> > +                   sizeof(d->shared_info->compat.evtchn_pending));
> > +            memset(&d->shared_info->native.evtchn_mask,
> > +                   0xff,
> > +                   sizeof(d->shared_info->native.evtchn_mask));
> > +
> > +            d->shared_info->native.arch.pfn_to_mfn_frame_list_list = 0;
> > +            for ( i = 0; i < XEN_LEGACY_MAX_VCPUS; i++ )
> > +                d->shared_info->native.vcpu_info[i].evtchn_pending_sel = 0;
> > +        }
> > +#else
> > +        memcpy(&d->shared_info->vcpu_info,
> > +               &shinfo->vcpu_info,
> > +               sizeof(d->shared_info->vcpu_info));
> > +        memcpy(&d->shared_info->arch,
> > +               &shinfo->arch,
> > +               sizeof(d->shared_info->shared));
> > +        memset(&d->shared_info->evtchn_pending,
> > +               0,
> > +               sizeof(d->shared_info->evtchn_pending));
> > +        memset(&d->shared_info->evtchn_mask,
> > +               0xff,
> > +               sizeof(d->shared_info->evtchn_mask));
> > +
> > +        d->shared_info.arch.pfn_to_mfn_frame_list_list = 0;
> > +        for ( i = 0; i < XEN_LEGACY_MAX_VCPUS; i++ )
> > +            d->shared_info.vcpu_info[i].evtchn_pending_sel = 0;
> > +#endif
> 
> A lot of redundancy; maybe it gets better if indeed you stop reading
> into an intermediate buffer.

As I said above, I think it is better if I continue to use an intermediate 
buffer but I'll see if I can add some macro magic to make this less verbose.

> 
> > +        xfree(shinfo);
> > +
> > +        rc = domain_load_end(c, false);
> > +    }
> > +    else
> > +        rc = domain_load_end(c, true);
> 
> Perhaps at least a brief comment here wouldn't hurt regarding the
> needs (or lack thereof) for HVM / Arm?
> 

Ok.

  Paul

> Jan