[XEN PATCH 1/7] xen: introduce XENFEAT_xenstore_late_init

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

From: Luca Miccio <lucmiccio@xxxxxxxxx>

Introduce a new feature flag to signal that xenstore will not be
immediately available at boot time. Instead, xenstore will become
available later, and a notification of xenstore readiness will be
signalled to the guest using the xenstore event channel.

Signed-off-by: Luca Miccio <lucmiccio@xxxxxxxxx>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/arm/include/asm/domain.h | 2 ++
 xen/common/kernel.c               | 2 ++
 xen/include/public/features.h     | 6 ++++++
 3 files changed, 10 insertions(+)

diff --git a/xen/arch/arm/include/asm/domain.h 
b/xen/arch/arm/include/asm/domain.h
index 9b3647587a..e5ae57cd09 100644
--- a/xen/arch/arm/include/asm/domain.h
+++ b/xen/arch/arm/include/asm/domain.h
@@ -89,6 +89,8 @@ struct arch_domain
 #ifdef CONFIG_TEE
     void *tee;
 #endif
+    /* Is this guest a dom0less domain? */
+    bool is_dom0less;
 }  __cacheline_aligned;
 
 struct arch_vcpu
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index e119e5401f..c00ea67e5f 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -550,6 +550,8 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             if ( is_hardware_domain(d) )
                 fi.submap |= 1U << XENFEAT_dom0;
 #ifdef CONFIG_ARM
+            if ( d->arch.is_dom0less )
+                fi.submap |= (1U << XENFEAT_xenstore_late_init);
             fi.submap |= (1U << XENFEAT_ARM_SMCCC_supported);
 #endif
 #ifdef CONFIG_X86
diff --git a/xen/include/public/features.h b/xen/include/public/features.h
index 9ee2f760ef..18f32b1a98 100644
--- a/xen/include/public/features.h
+++ b/xen/include/public/features.h
@@ -128,6 +128,12 @@
 #define XENFEAT_not_direct_mapped         16
 #define XENFEAT_direct_mapped             17
 
+/*
+ * The xenstore interface should be initialized only after receiving a
+ * xenstore event channel notification.
+ */
+#define XENFEAT_xenstore_late_init 18
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
2.25.1