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Re: [PATCH v3 7/7] xen/arm: introduce new xen,enhanced property value



Hi Rahul,

On 01/09/2022 10:13, Rahul Singh wrote:
Introduce a new "xen,enhanced" dom0less property value "no-xenstore" to
disable xenstore interface for dom0less guests.

Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
---
Changes in v3:
  - new patch in this version
---
  docs/misc/arm/device-tree/booting.txt |  4 ++++
  xen/arch/arm/domain_build.c           | 10 +++++++---
  xen/arch/arm/include/asm/kernel.h     |  3 +++
  3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/docs/misc/arm/device-tree/booting.txt 
b/docs/misc/arm/device-tree/booting.txt
index edef98e6d1..87f57f8889 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -204,6 +204,10 @@ with the following properties:
      - "disabled"
      Xen PV interfaces are disabled.
+ - no-xenstore
+    Xen PV interfaces, including grant-table will be enabled for the VM but
+    xenstore will be disabled for the VM.

NIT: I would drop one of the "for the VM" as it seems to be redundant.

+
      If the xen,enhanced property is present with no value, it defaults
      to "enabled". If the xen,enhanced property is not present, PV
      interfaces are disabled.
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 4b24261825..8dd9984225 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3336,10 +3336,14 @@ static int __init construct_domU(struct domain *d,
           (rc == 0 && !strcmp(dom0less_enhanced, "enabled")) )
      {
          if ( hardware_domain )
-            kinfo.dom0less_enhanced = true;
+            kinfo.dom0less_xenstore = true;
          else
-            panic("Tried to use xen,enhanced without dom0\n");
+            panic("Tried to use xen,enhanced without dom0 without 
no-xenstore\n");

This is a bit hard to parse. How about:

"At the moment, Xenstore support requires dom0 to be present"

      }
+    else if ( rc == 0 && !strcmp(dom0less_enhanced, "no-xenstore") )
+        kinfo.dom0less_xenstore = false;
+
+    kinfo.dom0less_enhanced = true;

Wouldn't this now set dom0less_enhanced unconditionally?

if ( vcpu_create(d, 0) == NULL )
          return -ENOMEM;
@@ -3379,7 +3383,7 @@ static int __init construct_domU(struct domain *d,
      if ( rc < 0 )
          return rc;
- if ( kinfo.dom0less_enhanced )
+    if ( kinfo.dom0less_xenstore )
      {
          ASSERT(hardware_domain);
          rc = alloc_xenstore_evtchn(d);
diff --git a/xen/arch/arm/include/asm/kernel.h 
b/xen/arch/arm/include/asm/kernel.h
index c4dc039b54..3d7fa94910 100644
--- a/xen/arch/arm/include/asm/kernel.h
+++ b/xen/arch/arm/include/asm/kernel.h
@@ -39,6 +39,9 @@ struct kernel_info {
      /* Enable PV drivers */
      bool dom0less_enhanced;
+ /* Enable Xenstore */
+    bool dom0less_xenstore;
+

AFAIU, it is not possible to have *_xenstore = true and *_enhanced = false. I think it would be clearer if ``dom0less_enhanced`` is turned to an enum with 3 values:
 - None
 - NOXENSTORE/BASIC
 - FULLY_ENHANCED

If we want to be future proof, I would use a field 'flags' where non-zero means enhanced. Each bit would indicate which features of Xen is exposed.

Cheers,

--
Julien Grall



 


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