Re: [Xen-devel] [PATCH V10 05/14] xen/pvh: balloon and grant changes.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 13 Dec 2013, Konrad Rzeszutek Wilk wrote:
> On Fri, Dec 13, 2013 at 02:49:15PM +0000, Stefano Stabellini wrote:
> > On Fri, 13 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > > On Fri, Dec 13, 2013 at 11:56:31AM +0000, Stefano Stabellini wrote:
> > > > On Thu, 12 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > > > > From: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> > > > > 
> > > > > For balloon changes we skip setting of local P2M as it's updated
> > > > > in Xen. For grant, the shared grant frame is the PFN and not MFN,
> > > > > hence its mapped via the same code path as HVM.
> > > > > 
> > > > > Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> > > > > [v1: Rebase on v3.7-rc3]
> > > > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > > > CC: <stefano.stabellini@xxxxxxxxxxxxx>
> > > > > Conflicts:
> > > > >       drivers/xen/balloon.c
> > > > > [v2: Rebase on v3.13-rc3 has lot of ARM changes.]
> > > > > ---
> > > > >  drivers/xen/balloon.c     |   37 
> > > > > ++++++++++++++++++++-----------------
> > > > >  drivers/xen/gntdev.c      |    3 ++-
> > > > >  drivers/xen/grant-table.c |   25 ++++++++++++++++++++++---
> > > > >  3 files changed, 44 insertions(+), 21 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > > > > index 55ea73f..0e9875a 100644
> > > > > --- a/drivers/xen/balloon.c
> > > > > +++ b/drivers/xen/balloon.c
> > > > > @@ -354,7 +354,9 @@ static enum bp_state 
> > > > > increase_reservation(unsigned long nr_pages)
> > > > >  
> > > > >  #ifdef CONFIG_XEN_HAVE_PVMMU
> > > > >               /* Link back into the page tables if not highmem. */
> > > > > -             if (xen_pv_domain() && !PageHighMem(page)) {
> > > > > +             if (xen_pv_domain() && !PageHighMem(page) &&
> > > > > +                 !xen_feature(XENFEAT_auto_translated_physmap)) {
> > > > > +
> > > > >                       int ret;
> > > > >                       ret = HYPERVISOR_update_va_mapping(
> > > > >                               (unsigned long)__va(pfn << PAGE_SHIFT),
> > > > > @@ -411,28 +413,29 @@ static enum bp_state 
> > > > > decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> > > > >  
> > > > >               scrub_page(page);
> > > > >  
> > > > > -             /*
> > > > > -              * Ballooned out frames are effectively replaced with
> > > > > -              * a scratch frame.  Ensure direct mappings and the
> > > > > -              * p2m are consistent.
> > > > > -              */
> > > > > -             scratch_page = get_balloon_scratch_page();
> > > > > +             if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> > > > > +                     unsigned long p;
> > > > > +
> > > > > +                     /*
> > > > > +                      * Ballooned out frames are effectively 
> > > > > replaced with
> > > > > +                      * a scratch frame.  Ensure direct mappings and 
> > > > > the
> > > > > +                      * p2m are consistent.
> > > > > +                      */
> > > > > +                     scratch_page = get_balloon_scratch_page();
> > > > >  #ifdef CONFIG_XEN_HAVE_PVMMU
> > > > > -             if (xen_pv_domain() && !PageHighMem(page)) {
> > > > > -                     ret = HYPERVISOR_update_va_mapping(
> > > > > -                             (unsigned long)__va(pfn << PAGE_SHIFT),
> > > > > -                             pfn_pte(page_to_pfn(scratch_page),
> > > > > +                     if (xen_pv_domain() && !PageHighMem(page)) {
> > > > > +                             ret = HYPERVISOR_update_va_mapping(
> > > > > +                                     (unsigned long)__va(pfn << 
> > > > > PAGE_SHIFT),
> > > > > +                                     
> > > > > pfn_pte(page_to_pfn(scratch_page),
> > > > >                                       PAGE_KERNEL_RO), 0);
> > > > > -                     BUG_ON(ret);
> > > > > -             }
> > > > > +                             BUG_ON(ret);
> > > > > +                     }
> > > > >  #endif
> > > > > -             if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> > > > > -                     unsigned long p;
> > > > >                       p = page_to_pfn(scratch_page);
> > > > >                       __set_phys_to_machine(pfn, pfn_to_mfn(p));
> > > > > -             }
> > > > > -             put_balloon_scratch_page();
> > > > >  
> > > > > +                     put_balloon_scratch_page();
> > > > > +             }
> > > > >               balloon_append(pfn_to_page(pfn));
> > > > >       }
> > > > 
> > > > These changes to balloon.c are similar to my patch but:
> > > > 
> > > > - they don't prevent set_phys_to_machine from being called by
> > > > increase_reservation for auto_translated guests
> > > 
> > > <nods>
> > > > 
> > > > - they don't prevent wasteful balloon_scratch_page from being allocated
> > > > for auto_translated guests
> > > 
> > > <nods>
> > > > 
> > > > I think that it would be best to take my patch instead.
> > > 
> > > Lets focus the review on your patch then and have it part of this
> > > series. 
> > 
> > OK, but keep in mind that Xen on ARMv8 is currently broken without that
> > patch.
> 
> Hm. We could have another patch to just disable BALLOON on ARMv8 :-)
> 
> The question you have to ask - if your patch causes regression are you
> OK tracking/fixing it over the holidays :-) If yes, then yes - we can
> put that in v3.13-rc3 to make it work properly on ARMv8.

Damn, that was a good argument.
After thinking more about it, I think that I, or a member of my team,
can actually fix possible bugs during the holidays. Especially
considering that the patch doesn't alter the behavior of PV guests.

So in short, yes :)

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