RE: [EXTERNAL] [PATCH v7 7/9] common/domain: add a domain context record for shared_info...

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 07 September 2020 08:01
> To: 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 v7 7/9] common/domain: add a domain context 
> record for shared_info...
> 
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> 
> 
> On 04.09.2020 19:29, Paul Durrant wrote:
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: 26 August 2020 14:58
> >>
> >> On 18.08.2020 12:30, Paul Durrant wrote:
> >>> v7:
> >>>  - Only restore vcpu_info and arch sub-structures for PV domains, to match
> >>>    processing of SHARED_INFO in xc_sr_restore_x86_pv.c
> >>
> >> Since you point out this original logic, ...
> >>
> >>> +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));
> >>> +        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));
> >>> +        }
> >>> +        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));
> >>> +        }
> >>> +#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));
> >>> +#endif
> >>
> >> ... where does the rest of that logic (resetting of
> >> arch.pfn_to_mfn_frame_list_list, evtchn_pending, evtchn_mask, and
> >> evtchn_pending_sel) get done? Or why is it not needed anymore?
> >
> > The resetting logic is still in xc_sr_restore_x86_pv.c (see patch #6).
> > It's going to need to stay there anyway to deal with older streams so
> > I made it common to both cases; it seems slightly separate from
> > restoring the shared info.
> 
> I guess I at least don't fully agree: The resetting is part of restoring,
> as it effectively determines which parts are restored and which parts
> are simply set (not truly reset, but I agree the perception may change
> depending on whose position you take). Hence at the very least this
> aspect wants clearly spelling out in the description, I think. But
> really I'd prefer if for old streams libxc took care of (all of) it,
> and if for new streams all logic lived in the hypervisor.
> 

Andrew, do you have an opinion either way?

  Paul

> Jan