linux-kernel - RE: [Xen-devel] Regressions in v3.3-rc1 introduced by "xen/granttable: Grant tables V2 implementation"

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Message-ID: <1327506706.24561.338.camel@zakaz.uk.xensource.com>
Date:	Wed, 25 Jan 2012 15:51:46 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Paul Durrant <Paul.Durrant@...rix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"annie.li@...cle.com" <annie.li@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Xen-devel] Regressions in v3.3-rc1 introduced by
 "xen/granttable: Grant tables V2 implementation"

On Wed, 2012-01-25 at 15:47 +0000, Ian Campbell wrote:
> On Wed, 2012-01-25 at 15:16 +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > 
> > > On HVM for gnttab_shared we make an add_to_physmap call with
> > > XENMAPSPACE_grant_table (in gnttab_map). I don't see any support call to
> > > do something similar for the status array though and I don't see a
> > > XENMAPSPACE_* specifically for that case either in the hypervisor either.
> > > 
> > 
> > There is no map-space for the status pages. To map them you use the
> > standard map space but OR a bit (top bit IIRC) into in the idx. It's a
> > bit icky, but that's how it is.
> 
> I can't see that happening anywhere in the current Linux tree, there's
> only one call to XENMAPSPACE_grant_table and it doesn't set the top bit,
> so presumably this is at least part of the problem.
> 
> I hope that "top bit" is consistent for 32 and 64 bit domains....

#define XENMAPIDX_grant_table_status 0x80000000

...so yes

Ian.

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