Re: [PATCH v2 1/2] altp2m: Merge p2m_set_altp2m_mem_access and p2m_set_mem_access

["Lengyel, Tamas" <tlengyel@novetta.com>]

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On Fri, Jan 29, 2016 at 4:03 AM, Jan Beulich <JBeulich@suse.com> wrote:

> >>> On 28.01.16 at 21:58, <tlengyel@novetta.com> wrote:
> > --- a/xen/arch/x86/mm/p2m.c
> > +++ b/xen/arch/x86/mm/p2m.c
> > @@ -1777,14 +1777,57 @@ bool_t p2m_mem_access_check(paddr_t gpa,
> unsigned long gla,
> >      return (p2ma == p2m_access_n2rwx);
> >  }
> >
> > +static int p2m_set_altp2m_mem_access(struct domain *d, struct
> p2m_domain *hp2m,
> > +                                     struct p2m_domain *ap2m,
> p2m_access_t a,
> > +                                     unsigned long gfn)
>
> I think new functions would better not use "unsigned long" for frame
> numbers.
>

The only place this is called from the gfn is already converted to unsigned
long. I don't see much point in converting it back to gfn_t and then back
to unsigned long again.. I was thinking this function may even be declared
as inline?


>
> > +{
> > +    mfn_t mfn;
> > +    p2m_type_t t;
> > +    p2m_access_t old_a;
> > +    unsigned int page_order;
> > +    int rc;
> > +
> > +    mfn = ap2m->get_entry(ap2m, gfn, &t, &old_a, 0, NULL, NULL);
> > +
> > +    /* Check host p2m if no valid entry in alternate */
> > +    if ( !mfn_valid(mfn) )
> > +    {
> > +        mfn = hp2m->get_entry(hp2m, gfn, &t, &old_a,
> > +                              P2M_ALLOC | P2M_UNSHARE, &page_order,
> NULL);
> > +
> > +        rc = -ESRCH;
> > +        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
> > +            goto out;
> > +
> > +        /* If this is a superpage, copy that first */
> > +        if ( page_order != PAGE_ORDER_4K )
> > +        {
> > +            unsigned long mask = ~((1UL << page_order) - 1);
> > +            gfn_t gfn2 = _gfn(gfn & mask);
> > +            mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
> > +
> > +            rc = ap2m->set_entry(ap2m, gfn_x(gfn2), mfn2, page_order,
> t, old_a, 1);
> > +            if ( rc )
> > +                goto out;
> > +        }
> > +    }
> > +
> > +    rc = ap2m->set_entry(ap2m, gfn, mfn, PAGE_ORDER_4K, t, a,
> > +                         (current->domain != d));
> > +
> > + out:
> > +    return rc;
> > +}
>
> With there not being any involved error handling here, I don't think
> using a label and goto is warranted here. But I'll leave the ultimate
> decision to George, of course.
>

RIght, this is a remnant from the previous version of this function where
out also had the p2m_unlock. Now that it is just a return I could do the
return in place of the gotos. Let me know which one is preferred.


>
> > --- a/xen/include/public/memory.h
> > +++ b/xen/include/public/memory.h
> > @@ -423,11 +423,14 @@ struct xen_mem_access_op {
> >      /* xenmem_access_t */
> >      uint8_t access;
> >      domid_t domid;
> > +    uint16_t altp2m_idx;
> > +    uint16_t _pad;
> >      /*
> >       * Number of pages for set op
> >       * Ignored on setting default access and other ops
> >       */
> >      uint32_t nr;
> > +    uint32_t _pad2;
>
> Repeating what I had said on v1: So this is a tools only interface,
> yes. But it's not versioned (other than e.g. domctl and sysctl), so
> altering the interface structure is at least fragile.
>

Not sure what I can do to address this.

Tamas

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