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

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Message-ID: <20131213145937.GB4770@phenom.dumpdata.com>
Date:	Fri, 13 Dec 2013 09:59:37 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	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, 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@...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.

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.
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