[PATCH v2] xen: Expose time_offset in struct arch_shared_info

["Tu Dinh" <ngoc-tu.dinh@xxxxxxxxxx>]

time_offset is currently always added to wc_sec. This means that without
the actual value of time_offset, guests have no way of knowing what's
the actual host clock. Once the guest clock drifts beyond 1 second,
updates to the guest RTC would themselves change time_offset and make it
impossible to resync guest time to host time.

Since there's no way to add more fields to struct shared_info, the
addition has to be done through struct arch_shared_info instead. Add two
fields in arch_shared_info representing time_offset's low and high
32-bit halves.

Provide a new feature bit XENFEAT_shared_info_time_offset for this
functionality.

Signed-off-by: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
---
v2: Remove unnecessary casts.
---
 tools/include/xen-foreign/reference.size | 5 ++---
 xen/common/kernel.c                      | 3 ++-
 xen/common/time.c                        | 5 +++++
 xen/include/public/arch-arm.h            | 2 ++
 xen/include/public/arch-ppc.h            | 3 +++
 xen/include/public/arch-riscv.h          | 3 ++-
 xen/include/public/arch-x86/xen.h        | 3 +++
 xen/include/public/features.h            | 5 +++++
 8 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/tools/include/xen-foreign/reference.size 
b/tools/include/xen-foreign/reference.size
index 11a06a7a43..38e799617a 100644
--- a/tools/include/xen-foreign/reference.size
+++ b/tools/include/xen-foreign/reference.size
@@ -9,6 +9,5 @@ vcpu_guest_context        |     352     352    2800    5168
 arch_vcpu_info            |       0       0      24      16
 vcpu_time_info            |      32      32      32      32
 vcpu_info                 |      48      48      64      64
-arch_shared_info          |       0       0      28      48
-shared_info               |    1088    1088    2344    3136
-
+arch_shared_info          |       8       8      36      56
+shared_info               |    1096    1096    2352    3144
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index fb45f81399..44af6f8f04 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -676,7 +676,8 @@ long do_xen_version(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
arg)
 #ifdef CONFIG_X86
                         (1U << XENFEAT_vcpu_time_phys_area) |
 #endif
-                        (1U << XENFEAT_runstate_phys_area);
+                        (1U << XENFEAT_runstate_phys_area) |
+                        (1U << XENFEAT_shared_info_time_offset);
             if ( VM_ASSIST(d, pae_extended_cr3) )
                 fi.submap |= (1U << XENFEAT_pae_pgdir_above_4gb);
             if ( paging_mode_translate(d) )
diff --git a/xen/common/time.c b/xen/common/time.c
index c873b5731b..6f1a8a11c2 100644
--- a/xen/common/time.c
+++ b/xen/common/time.c
@@ -118,6 +118,11 @@ void update_domain_wallclock_time(struct domain *d)
     shared_info(d, wc_sec_hi) = sec >> 32;
 #endif
 
+    shared_info(d, arch.time_offset) =
+        (uint32_t)d->time_offset.seconds;
+    shared_info(d, arch.time_offset_hi) =
+        (uint32_t)(d->time_offset.seconds >> 32);
+
     smp_wmb();
     *wc_version = version_update_end(*wc_version);
 
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index cd563cf706..4360f9835b 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -363,6 +363,8 @@ struct arch_vcpu_info {
 typedef struct arch_vcpu_info arch_vcpu_info_t;
 
 struct arch_shared_info {
+    uint32_t time_offset;
+    uint32_t time_offset_hi;
 };
 typedef struct arch_shared_info arch_shared_info_t;
 typedef uint64_t xen_callback_t;
diff --git a/xen/include/public/arch-ppc.h b/xen/include/public/arch-ppc.h
index b5e1a940a5..42ade11171 100644
--- a/xen/include/public/arch-ppc.h
+++ b/xen/include/public/arch-ppc.h
@@ -92,6 +92,9 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_guest_context_t);
 
 struct arch_shared_info {
     uint64_t boot_timebase;
+
+    uint32_t time_offset;
+    uint32_t time_offset_hi;
 };
 
 struct arch_vcpu_info {
diff --git a/xen/include/public/arch-riscv.h b/xen/include/public/arch-riscv.h
index 360d8e6871..286bf92473 100644
--- a/xen/include/public/arch-riscv.h
+++ b/xen/include/public/arch-riscv.h
@@ -65,8 +65,9 @@ struct arch_vcpu_info {
 };
 typedef struct arch_vcpu_info arch_vcpu_info_t;
 
-/* TODO:  add a placeholder entry if no real ones surface */
 struct arch_shared_info {
+    uint32_t time_offset;
+    uint32_t time_offset_hi;
 };
 typedef struct arch_shared_info arch_shared_info_t;
 
diff --git a/xen/include/public/arch-x86/xen.h 
b/xen/include/public/arch-x86/xen.h
index a7bf046ee0..401583383c 100644
--- a/xen/include/public/arch-x86/xen.h
+++ b/xen/include/public/arch-x86/xen.h
@@ -263,6 +263,9 @@ struct arch_shared_info {
     /* There's no room for this field in the generic structure. */
     uint32_t wc_sec_hi;
 #endif
+
+    uint32_t time_offset;
+    uint32_t time_offset_hi;
 };
 typedef struct arch_shared_info arch_shared_info_t;
 
diff --git a/xen/include/public/features.h b/xen/include/public/features.h
index 8801930947..b48591c17a 100644
--- a/xen/include/public/features.h
+++ b/xen/include/public/features.h
@@ -128,6 +128,11 @@
  */
 #define XENFEAT_dm_msix_all_writes        20
 
+/*
+ * arch_shared_info provides time_offset and time_offset_hi
+ */
+#define XENFEAT_shared_info_time_offset   21
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
2.43.0



--
Ngoc Tu Dinh | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech