linux-kernel - Re: [PATCH 5/6] xen/pvh: balloon and grant changes.

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Date:	Mon, 22 Oct 2012 12:04:56 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"mukesh.rathor@...cle.com" <mukesh.rathor@...cle.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: [PATCH 5/6] xen/pvh: balloon and grant changes.

On Mon, Oct 22, 2012 at 02:25:43PM +0100, Stefano Stabellini wrote:
> On Sat, 20 Oct 2012, 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>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ---
> >  drivers/xen/balloon.c     |   15 +++++++++------
> >  drivers/xen/gntdev.c      |    3 ++-
> >  drivers/xen/grant-table.c |   26 ++++++++++++++++++++++----
> >  3 files changed, 33 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > index 31ab82f..c825b63 100644
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -361,7 +361,9 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> >  		set_phys_to_machine(pfn, frame_list[i]);
> >  
> >  		/* 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)) {

This could be done as:

	if ((xen_pv_domain() && !PageHighMem(page) && !xen_feature(XENFEAT_auto_translated_physmap))

Just to make it more easier to read.

> > +
> >  			int ret;
> >  			ret = HYPERVISOR_update_va_mapping(
> >  				(unsigned long)__va(pfn << PAGE_SHIFT),
> > @@ -418,12 +420,13 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> >  		scrub_page(page);
> >  
> >  		if (xen_pv_domain() && !PageHighMem(page)) {
> > -			ret = HYPERVISOR_update_va_mapping(
> > -				(unsigned long)__va(pfn << PAGE_SHIFT),
> > -				__pte_ma(0), 0);
> > -			BUG_ON(ret);
> > +			if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> > +				ret = HYPERVISOR_update_va_mapping(
> > +					(unsigned long)__va(pfn << PAGE_SHIFT),
> > +					__pte_ma(0), 0);
> > +				BUG_ON(ret);
> > +			}
> >  		}
> 
> this change, unlike the one before, actually makes things different for
> traditional pv domains in case PageHighMem(page).

How? He is not altering the !PageHighMem check. Just adding a check
before the hypercall to render it nop on PVH.

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