Re: [Xen-devel] [PATCH 03/17] xen/mm: Move the MM types in a separate header

[Jan Beulich <jbeulich@suse.com>]

On 22.03.2020 17:14, julien@xen.org wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> It is getting incredibly difficult to use typesafe GFN/MFN/PFN in the
> headers because of circular dependency. For instance, asm-x86/page.h
> cannot include xen/mm.h.
> 
> In order to convert more code to use typesafe, the types are now moved
> in a separate header that requires only a few dependencies.

We definitely need to do this, so thanks for investing the
time. I think though that we want to settle up front (and
perhaps record in a comment in the new header) what is or
is not suitable to go into the new header. After all you're
moving not just type definitions, but also simple helper
functions.

> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -1,50 +1,7 @@
>  /******************************************************************************
>   * include/xen/mm.h
>   *
> - * Definitions for memory pages, frame numbers, addresses, allocations, etc.
> - *
>   * Copyright (c) 2002-2006, K A Fraser <keir@xensource.com>
> - *
> - *                         +---------------------+
> - *                          Xen Memory Management
> - *                         +---------------------+
> - *
> - * Xen has to handle many different address spaces.  It is important not to
> - * get these spaces mixed up.  The following is a consistent terminology which
> - * should be adhered to.
> - *
> - * mfn: Machine Frame Number
> - *   The values Xen puts into its own pagetables.  This is the host physical
> - *   memory address space with RAM, MMIO etc.
> - *
> - * gfn: Guest Frame Number
> - *   The values a guest puts in its own pagetables.  For an auto-translated
> - *   guest (hardware assisted with 2nd stage translation, or shadowed), gfn !=
> - *   mfn.  For a non-translated guest which is aware of Xen, gfn == mfn.
> - *
> - * pfn: Pseudophysical Frame Number
> - *   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 device DMA address space. All initiators for
> - *   (i.e. all devices assigned to) a guest share a single DMA address space
> - *   and, by default, Xen will ensure dfn == pfn.
> - *
> - * WARNING: Some of these terms have changed over time while others have been
> - * used inconsistently, meaning that a lot of existing code does not match the
> - * definitions above.  New code should use these terms as described here, and
> - * over time older code should be corrected to be consistent.
> - *
> - * An incomplete list of larger work area:
> - * - Phase out the use of 'pfn' from the x86 pagetable code.  Callers should
> - *   know explicitly whether they are talking about mfns or gfns.
> - * - Phase out the use of 'pfn' from the ARM mm code.  A cursory glance
> - *   suggests that 'mfn' and 'pfn' are currently used interchangeably, where
> - *   'mfn' is the appropriate term to use.
> - * - Phase out the use of gpfn/gmfn where pfn/mfn are meant.  This excludes
> - *   the x86 shadow code, which uses gmfn/smfn pairs with different,
> - *   documented, meanings.
>   */
>  
>  #ifndef __XEN_MM_H__
> @@ -54,100 +11,11 @@
>  #include <xen/types.h>
>  #include <xen/list.h>
>  #include <xen/spinlock.h>
> -#include <xen/typesafe.h>
>  #include <xen/kernel.h>
> +#include <xen/mm_types.h>

Is there anything left in the header here which requires the
explicit inclusion of xen/kernel.h?

Jan