Re: [Xen-devel] [PATCH v8 1/7] iommu: introduce the concept of DFN...

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf
> Of Paul Durrant
> Sent: 13 September 2018 14:09
> To: 'Jan Beulich' <JBeulich@xxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Julien Grall
> <julien.grall@xxxxxxx>; Suravee Suthikulpanit
> <suravee.suthikulpanit@xxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v8 1/7] iommu: introduce the concept of
> DFN...
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: 13 September 2018 13:46
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>; Julien Grall
> > <julien.grall@xxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Kevin Tian
> > <kevin.tian@xxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> xen-
> > devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> > Subject: Re: [PATCH v8 1/7] iommu: introduce the concept of DFN...
> >
> > >>> On 13.09.18 at 12:31, <paul.durrant@xxxxxxxxxx> wrote:
> > > ...meaning 'device DMA frame number' i.e. a frame number mapped in the
> > IOMMU
> > > (rather than the MMU) and hence used for DMA address translation.
> > >
> > > This patch is a largely cosmetic change that substitutes the terms
> 'gfn'
> > > and 'gaddr' for 'dfn' and 'daddr' in all the places where the frame
> > number
> > > or address relate to a device rather than the CPU.
> > >
> > > The parts that are not purely cosmetic are:
> > >
> > >  - the introduction of a type-safe declaration of dfn_t and definition
> > of
> > >    INVALID_DFN to make the substitution of gfn_x(INVALID_GFN)
> > mechanical.
> > >  - the introduction of __dfn_to_daddr and __daddr_to_dfn (and type-
> safe
> > >    variants without the leading __) with some use of the former.
> >
> > The latter is rather unfortunate, but presumably unavoidable,
> > both because of the name space issue and the fact that the other
> > non-type-safe variants are intended to go away as well).
> >
> > > --- a/xen/include/xen/iommu.h
> > > +++ b/xen/include/xen/iommu.h
> > > @@ -23,11 +23,37 @@
> > >  #include <xen/page-defs.h>
> > >  #include <xen/spinlock.h>
> > >  #include <xen/pci.h>
> > > +#include <xen/typesafe.h>
> > >  #include <public/hvm/ioreq.h>
> > >  #include <public/domctl.h>
> > >  #include <asm/device.h>
> > >  #include <asm/iommu.h>
> > >
> > > +TYPE_SAFE(uint64_t, dfn);
> > > +#define PRI_dfn     PRIx64
> > > +#define INVALID_DFN _dfn(~0ULL)
> > > +
> > > +#ifndef dfn_t
> > > +#define dfn_t /* Grep fodder: dfn_t, _dfn() and dfn_x() are defined
> > above */
> > > +#define _dfn
> > > +#define dfn_x
> > > +#undef dfn_t
> > > +#undef _dfn
> > > +#undef dfn_x
> > > +#endif
> > > +
> > > +#define IOMMU_PAGE_SHIFT 12
> >
> > Is this correct for ARM in all cases?
> 
> Looks like there's no fixed page size so these may actually be better off
> in an x86 header. They just got pulled here when I made the code common.
> 
> >
> > > +#define IOMMU_PAGE_SIZE  (1 << IOMMU_PAGE_SHIFT)
> > > +#define IOMMU_PAGE_MASK  (~(IOMMU_PAGE_SIZE - 1))
> > > +
> > > +typedef uint64_t daddr_t;
> > > +
> > > +#define __dfn_to_daddr(dfn) ((daddr_t)(dfn) << IOMMU_PAGE_SHIFT)
> > > +#define __daddr_to_dfn(daddr) ((uint64_t)(daddr >> IOMMU_PAGE_SHIFT))
> >
> > Please could at least the latter of the two casts be omitted? Also
> > daddr needed parenthesizing.
> >
> 
> Ok.
> 
> > > --- a/xen/include/xen/mm.h
> > > +++ b/xen/include/xen/mm.h
> > > @@ -26,6 +26,11 @@
> > >   *   A linear idea of a guest physical address space. For an auto-
> > translated
> > >   *   guest, pfn == gfn while for a non-translated guest, pfn != gfn.
> > >   *
> > > + * dfn: Device DMA Frame Number (definitions in include/xen/iommu.h)
> > > + *   The linear frame numbers of IOMMU address space. All initiators
> > for (i.e.
> > > + *   all devices assigned to) a guest share a single IOMMU address
> > space and,
> > > + *   by default, Xen will ensure dfn == pfn.
> >
> > While the names have been changed, the test still talks about "IOMMU
> > address space". In particular for the IOMMU there very clear are two
> > address spaces (incoming and outgoing), so this needs disambiguation.
> >
> > With these minor issues taken care of
> > Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> >
> 
> Thanks. Do you want me to move the page size definitions and re-submit
> with the other things fixed up?
> 

Actually I just pulled staging and the series needs a re-base (again) anyway, 
so I'll submit v9.

  Paul

> > Jan
> >
> 
> 
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