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Re: [Xen-devel] [RFC PATCH V2 1/26] VIOMMU: Add vIOMMU helper functions to create, destroy and query capabilities



Hi Jan,

On 06/06/17 07:31, Jan Beulich wrote:
On 02.06.17 at 09:31, <julien.grall@xxxxxxx> wrote:
On 06/02/2017 08:10 AM, Lan Tianyu wrote:
On 2017年05月30日 23:42, Jan Beulich wrote:
On 30.05.17 at 17:36,<wei.liu2@xxxxxxxxxx>  wrote:
On Thu, May 18, 2017 at 01:34:31AM -0400, Lan Tianyu wrote:
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -73,6 +73,17 @@ config TMEM

          If unsure, say Y.

+config VIOMMU
+       def_bool y
+       prompt "Xen vIOMMU Support" if EXPERT = "y"
+       depends on X86
+       ---help---
+        Virtual IOMMU provides interrupt remapping function for guest and
+        it allows guest to boot up more than 255 vcpus which requires interrupt
+        remapping function.
+
+         If unsure, say Y.
Indentation. And this should be disabled by default.
It's actually a question whether in our current scheme a Kconfig
option is appropriate here in the first place. I'd rather see this be
an always built feature which needs enabling on the command line
for the time being.

           In the RFC V1, we made vIOMMU always built-in feature. But
ARM or other arches doesn't have vIOMMU support.

Julien suggested to introduce a new Kconfig and only built vIOMMU on
x86. Both two ways won't affect vIOMMU function.

https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxx/msg101421.html

Jan & Julien, we need to make a choice here
We should definitely not compiled in code that are not used for an
architecture. This would be dead code or potential bug if not disabled
correctly.

I agree, but imo this should be a prompt-less Kconfig option,
selected under suitable conditions.

I don't mind of the way to do it as long as it is disabled on ARM.

Cheers,

--
Julien Grall

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