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

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Date:	Fri, 13 Dec 2013 14:49:15 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	<george.dunlap@...citrix.com>, <ian.jackson@...citrix.com>,
	<mukesh.rathor@...cle.com>, <tim@....org>, <jbeulich@...e.com>,
	<boris.ostrovsky@...cle.com>, <david.vrabel@...rix.com>
Subject: Re: [PATCH V10 05/14] xen/pvh: balloon and grant changes.

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@...cle.com>
> > > 
> > > 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@...cle.com>
> > > [v1: Rebase on v3.7-rc3]
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > > CC: <stefano.stabellini@...citrix.com>
> > > 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.
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