Re: [PATCH for-next 8/9] xen: Introduce HAS_M2P config and use to protect mfn_to_gmfn call

From: Wei Liu <wei.liu2@citrix.com>
To: Julien Grall <julien.grall@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
	oleksandr_tyshchenko@epam.com, Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"andrii_anisov@epam.com" <andrii_anisov@epam.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH for-next 8/9] xen: Introduce HAS_M2P config and use to protect mfn_to_gmfn call
Date: Thu, 18 Apr 2019 12:46:27 +0100	[thread overview]
Message-ID: <20190418114627.GC30543@zion.uk.xensource.com> (raw)
In-Reply-To: <fefbf936-c28d-8ae9-0560-8c0b0d6bc75a@arm.com>

On Wed, Apr 17, 2019 at 06:42:47PM +0100, Julien Grall wrote:
> Hi,
> 
> @Wei, @Ian: Do you have any input?

Sorry I haven't been following this closely, but shouldn't we fix the
interface to return gfn instead? And then the mapping of it should
interpret the value properly per guest type.

I don't see immediately how user space program will need to access this
page for autotranslated guests though.

Wei.

> 
> On 14/03/2019 07:55, Jan Beulich wrote:
> > > > > On 13.03.19 at 18:30, <julien.grall@arm.com> wrote:
> > > On 13/03/2019 15:20, Jan Beulich wrote:
> > > > > > > On 18.02.19 at 12:35, <julien.grall@arm.com> wrote:
> > > > > --- a/xen/common/domctl.c
> > > > > +++ b/xen/common/domctl.c
> > > > > @@ -205,7 +205,7 @@ void getdomaininfo(struct domain *d, struct
> > > xen_domctl_getdomaininfo *info)
> > > > >        info->outstanding_pages = d->outstanding_pages;
> > > > >        info->shr_pages         = atomic_read(&d->shr_pages);
> > > > >        info->paged_pages       = atomic_read(&d->paged_pages);
> > > > > -    info->shared_info_frame = mfn_to_gmfn(d, virt_to_mfn(d->shared_info));
> > > > > +    info->shared_info_frame = gfn_x(domain_shared_info_gfn(d));
> > > > 
> > > > I think this change wants to be accompanied by a warning attached
> > > > to the field declaration in the public header.
> > > 
> > > Make sense.
> > > 
> > > > 
> > > > But I'd also like to have the tool stack maintainers' view on making
> > > > this field effectively unusable for Arm.
> > > 
> > > The value in shared_info_frame was plain wrong since the creation of Xen Arm. So
> > > this is just making the error more obvious. I don't expect any user of it on Arm.
> > 
> > Well, my request for tool stack maintainer input wasn't to put under
> > question that the field can't currently be used sensibly on Arm.
> > Instead I'm meaning to know whether it can be sensibly expected
> > for the tool stack to want to use the field uniformly, in which case
> > rather than making it more obviously not work it should be fixed
> > instead.
> > 
> > Jan
> > 
> > 
> 
> -- 
> Julien Grall

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