Re: [Xen-devel] [PATCH v6 7/9] xen/mem_access: Use __get_gfn_type_access in set_mem_access

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

On Wed, Jan 29, 2020 at 6:10 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 27.01.2020 19:06, Tamas K Lengyel wrote:
> > Use __get_gfn_type_access instead of p2m->get_entry to trigger page-forking
> > when the mem_access permission is being set on a page that has not yet been
> > copied over from the parent.
>
> You talking of page-forking here, don't you mean ...
>
> > --- a/xen/arch/x86/mm/mem_access.c
> > +++ b/xen/arch/x86/mm/mem_access.c
> > @@ -303,11 +303,10 @@ static int set_mem_access(struct domain *d, struct 
> > p2m_domain *p2m,
> >      ASSERT(!ap2m);
> >  #endif
> >      {
> > -        mfn_t mfn;
> >          p2m_access_t _a;
> >          p2m_type_t t;
> > -
> > -        mfn = p2m->get_entry(p2m, gfn, &t, &_a, 0, NULL, NULL);
> > +        mfn_t mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &t, &_a,
> > +                                          P2M_ALLOC, NULL, false);
>
> ... P2M_UNSHARE here?

No, P2M_UNSHARE is only required if you are doing a memory write.
Setting memory access permissions is not a memory write, so it's
sufficient to just allocate the p2m entry. P2M_ALLOCATE also
encompasses forking the entry if there is a parent VM.

>
> Also shouldn't you have Cc-ed Petre and Alexandru on this patch
> (for their R: entries) and at least George (perhaps also Andrew
> and me) to get an ack, seeing that you're the only maintainer
> of the file?

I've ran ./add_maintainers.pl on the patches, not sure why noone else got CC-d.

Tamas

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