[Xen-devel] Xen's Linux kernel config options v3

["Luis R. Rodriguez" <mcgrof@xxxxxxxx>]

This is a third respin for a design proposal for a rework on the config options
on the Linux kernel related to Xen. The frist two proposals came from Juergen,
I'm taking on the work now as some other work I am doing is related to this.
This third iteration addresses the feedback given on Juergen's last v2
proposal. Let me know if there are any questions or any further feedback before
we start addressing the changes.

Reasons to consider a cleanup / reorganizing of the kconfig options:

- Everything depends on Xen but that's obviously not right. For instance
  we want to be able to build Xen frontend drivers for HVM domains without
  the need for choosing a pvops kernel: currently the frontend drivers need
  Xen configured which depends on PARAVIRT.
- XEN should not depend on PAE, we can have HVM guests without PAE.
- Some features are available for x86 only, in spite of these not being
  architecture specific, e.g. XEN_DEBUG_FS
- Be able to build a Dom0 using XEN_PVH(x86) without having to configure
  XEN_HAVE_PVMMU(x86).

Current Xen related config options are as follows:

Legend:

- The first column are the Xen config options. Indentation in this
  column reflects the dependency between those options (e.g.
  XEN_SCSI_BACKEND depends on XEN_BACKEND, which in turn depends on
  XEN_DOM0, which depends on XEN).
- The second column shows the options which are selected automatically
  if the corresponding option in the first column is configured.
- The last column shows additional dependencies which can't be shown via
  the indentation level of the first column.
- Some options or dependencies are architecture specific, they are
  listed with the architecture requirements in parens (e.g. XEN_TMEM(x86)
  which is available for x86 only).
- Non-Xen options are mentioned only if they seem to be really relevant,
  like e.g. PARAVIRT or BROKEN.
- All listed options are user selectable, options which are not user selectable 
but
  automatic are prefixed with a '*' on the left hand side to make emphasis

Option                          Selects                 Depends
---------------------------------------------------------------------
XEN                             PARAVIRT_CLOCK(x86)     PARAVIRT(x86)
                                XEN_HAVE_PVMMU(x86)
                                SWIOTLB_XEN(arm,arm64)
  PCI_XEN(x86)                  SWIOTLB_XEN
  XEN_DOM0                                              PCI_XEN(x86)
    XEN_BACKEND
      XEN_BLKDEV_BACKEND
      XEN_PCIDEV_BACKEND(x86)
      XEN_SCSI_BACKEND
      XEN_NETDEV_BACKEND
    XEN_ACPI_HOTPLUG_MEMORY                             XEN_STUB
    XEN_ACPI_HOTPLUG_CPU                                XEN_STUB
    XEN_MCE_LOG(x86)
  XEN_ACPI_PROCESSOR(x86)                               ACPI_PROCESSOR
                                                        CPU_FREQ
  XEN_PVHVM(x86)
    XEN_PVH(x86)
  XEN_MAX_DOMAIN_MEMORY(x86)
  XEN_SAVE_RESTORE(x86)
  XEN_DEBUG_FS(x86)
  XEN_FBDEV_FRONTEND            XEN_XENBUS_FRONTEND
                                INPUT_XEN_KBDDEV_FRONTEND
  XEN_BLKDEV_FRONTEND           XEN_XENBUS_FRONTEND
  HVC_XEN
    HVC_XEN_FRONTEND            XEN_XENBUS_FRONTEND
  TCG_XEN                       XEN_XENBUS_FRONTEND
  XEN_PCIDEV_FRONTEND           PCI_XEN
                                XEN_XENBUS_FRONTEND
  XEN_SCSI_FRONTEND             XEN_XENBUS_FRONTEND
  INPUT_XEN_KBDDEV_FRONTEND     XEN_XENBUS_FRONTEND
  XEN_WDT
  XEN_BALLOON
    XEN_SELFBALLOONING                                  XEN_TMEM
    XEN_BALLOON_MEMORY_HOTPLUG
    XEN_SCRUB_PAGES
  XEN_DEV_EVTCHN
  XENFS                         XEN_PRIVCMD
    XEN_COMPAT_XENFS
  XEN_SYS_HYPERVISOR
  XEN_XENBUS_FRONTEND
  XEN_GNTDEV
  XEN_GRANT_DEV_ALLOC
  SWIOTLB_XEN
  XEN_TMEM(x86)
  XEN_PRIVCMD
  XEN_STUB(x86_64)                                      BROKEN
  XEN_ACPI_PROCESSOR(x86)
  XEN_HAVE_PVMMU
  XEN_EFI(x64)
  XEN_NETDEV_FRONTEND           XEN_XENBUS_FRONTEND

After some feedback for the first draft I'd suggest the following:

Option                          Selects                 Depends
----------------------------------------------------------------------
XEN
  XEN_PV(x86)                   XEN_HAVE_PVMMU(x86)
                                PARAVIRT
                                PARAVIRT_CLOCK
  XEN_PVH(x86)                  XEN_PVHVM
                                PARAVIRT
                                PARAVIRT_CLOCK
  XEN_PVHVM(x86)                PARAVIRT
                                PARAVIRT_CLOCK
  XEN_BACKEND                   SWIOTLB_XEN(arm,arm64)  XEN_PV(x86) ||
                                                        XEN_PVH(x86) ||
                                                        XEN_PVHVM(x86)
                                XEN_TMEM(x86)
                                XEN_PRIVCMD
    XEN_BLKDEV_BACKEND
    XEN_PCIDEV_BACKEND(x86)
    XEN_SCSI_BACKEND
    XEN_NETDEV_BACKEND
  PCI_XEN(x86)                  SWIOTLB_XEN
  XEN_DOM0                      XEN_BACKEND             XEN_PV(x86) ||
                                PCI_XEN(x86)            XEN_PVH(x86)
    XEN_ACPI_HOTPLUG_MEMORY                             XEN_STUB
    XEN_ACPI_HOTPLUG_CPU                                XEN_STUB
    XEN_MCE_LOG(x86)
    XEN_ACPI_PROCESSOR(x86)                             ACPI_PROCESSOR
                                                        CPU_FREQ
    XEN_SAVE_RESTORE(x86)
    XEN_DEBUG_FS
    XEN_WDT
  XEN_MAX_DOMAIN_MEMORY(x86)                            XEN_HAVE_PVMMU(x86)
  XEN_BALLOON
    XEN_SELFBALLOONING                                  XEN_TMEM(x86)
    XEN_BALLOON_MEMORY_HOTPLUG
    XEN_SCRUB_PAGES
  XENFS                         XEN_PRIVCMD
    XEN_COMPAT_XENFS
  XEN_SYS_HYPERVISOR
  XEN_DEV_EVTCHN
  XEN_GNTDEV
  XEN_GRANT_DEV_ALLOC
  SWIOTLB_XEN
  XEN_STUB(x86_64)                                      BROKEN
  XEN_ACPI_PROCESSOR(x86)
 *XEN_HAVE_PVMMU(x86)                                   XEN_PV(x86)
  XEN_EFI(x64)
  XEN_XENBUS_FRONTEND
XEN_FRONTEND                    XEN
                                XEN_XENBUS_FRONTEND
  XEN_FBDEV_FRONTEND            INPUT_XEN_KBDDEV_FRONTEND
  XEN_BLKDEV_FRONTEND
  HVC_XEN_FRONTEND              HVC_XEN
  TCG_XEN
  XEN_PCIDEV_FRONTEND(x86)      PCI_XEN(x86)
  XEN_SCSI_FRONTEND
  INPUT_XEN_KBDDEV_FRONTEND
  XEN_NETDEV_FRONTEND
  XEN_PLATFORM_PCI(x86)

Changes since v2:

 * Add XEN_ACPI_PROCESSOR (Konrad)
 * XEN_MAX_DOMAIN_MEMORY(x86) depends on XEN_HAVE_PVMMU(x86) now (Juergen).
   Juergen will later replace this once he adds > 500 GiB pv-domains
 * Clarifications on some lose options, we seem to want to keep these
   user selectable to be able to allow userspace options which do not depend
   on xen backend / frontends: ballooning, xenfs, sysfs, event dev, gntdev (Jan)
 * Tons of clarifications on x86 specific options (Stefano), this includes
   XEN_PVHVM(x86)

  Luis

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