Re: [Xen-devel] [PATCH v2 3/7] xen/vm-events: Move monitor_domctl to common-side.

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Wed, Feb 10, 2016 at 10:34 AM, Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx> wrote:

On 2/10/2016 6:39 PM, Tamas K Lengyel wrote:

On Wed, Feb 10, 2016 at 8:52 AM, Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx> wrote:

1. Kconfig:
 * Added Kconfigs for common monitor vm-events:
 # see files: common/Kconfig, x86/Kconfig
  HAS_VM_EVENT_WRITE_CTRLREG
  HAS_VM_EVENT_SINGLESTEP
  HAS_VM_EVENT_SOFTWARE_BREAKPOINT
  HAS_VM_EVENT_GUEST_REQUEST

2. Moved monitor_domctl from arch-side to common-side
 2.1. Moved arch/x86/monitor.c to common/monitor.c
  # see files: arch/x86/Makefile, xen/common/Makefile, xen/common/monitor.c
  # changes:
    - removed status_check (we would have had to duplicate it in X86
      arch_monitor_domctl_event otherwise)
    - moved get_capabilities to arch-side (arch_monitor_get_capabilities)
    - moved XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP to arch-side (see
      arch_monitor_domctl_op)
    - put XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR to x86-side (see
      arch_monitor_domctl_event)
    - surrounded switch cases w/ CONFIG_HAS_VM_EVENT_*

 2.2. Moved asm-x86/monitor.h to xen/monitor.h
  # see files: arch/x86/hvm/event.c, arch/x86/hvm/hvm.c,
        Âarch/x86/hvm/vmx/vmx.c, xen/common/domctl.c

 2.3. Removed asm-arm/monitor.h (no longer needed)

3. Added x86/monitor_x86.c => will rename in next commit to monitor.c (not done
in this commit to avoid git seeing this as being the modified old monitor.c =>
keeping the same name would have rendered an unnecessarily bulky diff)
  # see files: arch/x86/Makefile
  # implements X86-side arch_monitor_domctl_event

4. Added asm-x86/monitor_arch.h, asm-arm/monitor_arch.h (renamed to
monitor.h in next commit, reason is the same as @ (3.).
  # define/implement: arch_monitor_get_capabilities, arch_monitor_domctl_op
    and arch_monitor_domctl_event

So these commit messages are not very good IMHO. Rather then just summarizing what the patch does you should describe why the patch is needed in the first place. Usually for longer series having a cover page is also helpful to outline how the patches in the series fit together.

The intention was to make review easier (following the changes in parallel w/
the commit message). But indeed I was maybe too focused on that, should have
started w/ stating the purpose of these changes rather than jumping directly to detailing
them. Will try to compact these commit messages next time (maybe move details to the
introductory section instead, as you suggest).

Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
---
Âxen/arch/x86/Kconfig               | Â4 +
Âxen/arch/x86/Makefile              Â| Â2 +-
Âxen/arch/x86/hvm/event.c             | Â2 +-
Âxen/arch/x86/hvm/hvm.c              | Â2 +-
Âxen/arch/x86/hvm/vmx/vmx.c            | Â2 +-
Âxen/arch/x86/monitor_x86.c            | 72 ++++++++
Âxen/common/Kconfig                | 20 +++
Âxen/common/Makefile               Â| Â1 +
Âxen/common/domctl.c               Â| Â2 +-
Âxen/{arch/x86 => common}/monitor.c        | 195 +++++++++-------------
Âxen/include/asm-arm/{monitor.h => monitor_arch.h} |Â 34 +++-
Âxen/include/asm-x86/monitor_arch.h        | 74 ++++++++
Âxen/include/{asm-x86 => xen}/monitor.h      | 17 +-
Â13 files changed, 293 insertions(+), 134 deletions(-)
Âcreate mode 100644 xen/arch/x86/monitor_x86.c
Ârename xen/{arch/x86 => common}/monitor.c (44%)
Ârename xen/include/asm-arm/{monitor.h => monitor_arch.h} (46%)
Âcreate mode 100644 xen/include/asm-x86/monitor_arch.h
Ârename xen/include/{asm-x86 => xen}/monitor.h (74%)

diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 3a90f47..e46be1b 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -14,6 +14,10 @@ config X86
    select HAS_MEM_ACCESS
    select HAS_MEM_PAGING
    select HAS_MEM_SHARING
+Â Â Â Âselect HAS_VM_EVENT_WRITE_CTRLREG

You mentioned in the previous revision of this series that currently you only have plans to implement write_ctrleg and guest_request events for ARM. I think singlestep and software_breakpoint should not be moved to common without a clear plan to have those implemented. Now, if you were to include the implementation of write_ctrlreg and guest_request in this series and leave the others in x86 as they are now, I don't think there would be any reason to have these Kconfig options present at all.

Moving what made sense to be moved to common was a suggestion of Ian's.
The purpose of this patch is to --avoid-- having to go through this process again
when an implementation of feature X for architecture A != X86 comes into place.
IMHO what is common should stay in common and I don't see any issues w/
having them there, only advantages (future implementations of these features will
be easier).
Maybe Ian can chime in on this.

That's the upside. The downside is that in the interim, while those features are not implemented, we need to add a bunch of Kconfig variables to decide under what build they are available. If it was moved to common only when the feature is available for all architectures, we wouldn't need that many ifdefs and the code would be clearer. So I do see why it would be beneficial having these moved to common now, but I still rather have it happen when it's necessary and without the Kconfig settings.

Tamas

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