RE: [PATCH v4 07/14] iommu: make map, unmap and flush all take both an order and a count

From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jan Beulich <jbeulich@suse.com>, Paul Durrant <paul@xen.org>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Paul Durrant" <pdurrant@amazon.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	"Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>
Subject: RE: [PATCH v4 07/14] iommu: make map, unmap and flush all take both an order and a count
Date: Fri, 14 Aug 2020 06:57:05 +0000	[thread overview]
Message-ID: <MWHPR11MB1645A1F08A8174FF19C9A98B8C400@MWHPR11MB1645.namprd11.prod.outlook.com> (raw)
In-Reply-To: <2765087f-4168-191d-c547-cbc2e74d3fee@suse.com>

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Thursday, August 6, 2020 5:57 PM
> 
> On 04.08.2020 15:42, Paul Durrant wrote:
> > From: Paul Durrant <pdurrant@amazon.com>
> >
> > At the moment iommu_map() and iommu_unmap() take a page order but
> not a
> > count, whereas iommu_iotlb_flush() takes a count but not a page order.
> > This patch simply makes them consistent with each other.
> 
> Why can't we do with just a count, where order gets worked out by
> functions knowing how to / wanting to deal with higher order pages?

Agree. especially the new map/unmap code looks weird when having both 
order and count in parameters.

Thanks
Kevin

> 
> > --- a/xen/arch/x86/mm/p2m-ept.c
> > +++ b/xen/arch/x86/mm/p2m-ept.c
> > @@ -843,7 +843,7 @@ out:
> >           need_modify_vtd_table )
> >      {
> >          if ( iommu_use_hap_pt(d) )
> > -            rc = iommu_iotlb_flush(d, _dfn(gfn), (1u << order),
> > +            rc = iommu_iotlb_flush(d, _dfn(gfn), (1u << order), 1,
> 
> Forgot to drop the "1 << "? (There are then I think two more instances
> further down.)
> 
> > --- a/xen/common/memory.c
> > +++ b/xen/common/memory.c
> > @@ -851,12 +851,12 @@ int xenmem_add_to_physmap(struct domain *d,
> struct xen_add_to_physmap *xatp,
> >
> >          this_cpu(iommu_dont_flush_iotlb) = 0;
> >
> > -        ret = iommu_iotlb_flush(d, _dfn(xatp->idx - done), done,
> > +        ret = iommu_iotlb_flush(d, _dfn(xatp->idx - done), 0, done,
> 
> Arguments wrong way round? (This risk of inverting their order is
> one of the primary reasons why I think we want just a count.) I'm
> also uncertain about the use of 0 vs PAGE_ORDER_4K here.
> 
> >                                  IOMMU_FLUSHF_added | IOMMU_FLUSHF_modified);
> >          if ( unlikely(ret) && rc >= 0 )
> >              rc = ret;
> >
> > -        ret = iommu_iotlb_flush(d, _dfn(xatp->gpfn - done), done,
> > +        ret = iommu_iotlb_flush(d, _dfn(xatp->gpfn - done), 0, done,
> 
> Same here then.
> 
> Jan