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Re: [PATCH 2/5] iommu / domctl: introduce XEN_DOMCTL_iommu_ctl



Hi Paul,

On 19/10/2020 08:23, Paul Durrant wrote:
-----Original Message-----
From: Julien Grall <julien@xxxxxxx>
Sent: 16 October 2020 16:47
To: Paul Durrant <paul@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Paul Durrant <pdurrant@xxxxxxxxxx>; Daniel De Graaf 
<dgdegra@xxxxxxxxxxxxx>; Ian Jackson
<iwj@xxxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper 
<andrew.cooper3@xxxxxxxxxx>; George Dunlap
<george.dunlap@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Stefano Stabellini
<sstabellini@xxxxxxxxxx>
Subject: Re: [PATCH 2/5] iommu / domctl: introduce XEN_DOMCTL_iommu_ctl

Hi Paul,

On 05/10/2020 10:49, Paul Durrant wrote:
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 791f0a2592..75e855625a 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1130,6 +1130,18 @@ struct xen_domctl_vuart_op {
                                    */
   };

+/*
+ * XEN_DOMCTL_iommu_ctl
+ *
+ * Control of VM IOMMU settings
+ */
+
+#define XEN_DOMCTL_IOMMU_INVALID 0

I can't find any user of XEN_DOMCTL_IOMMU_INVALID. What's the purpose
for it?


It's just a placeholder. I think it's generally safer that a zero opcode value 
is invalid.

Thanks for the explanation. I first thought the goal would to somehow invalidate the IOMMU :).

Anyway, it might be worth adding /* Reserved - should never be used */ on top.

Cheers,

--
Julien Grall



 


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