[PATCH 08/13] xen: XEN_DOMCTL_gethvmcontext hypercall

[Andrew Cooper <andrew.cooper3@citrix.com>]

The semantics of XEN_DOMCTL_gethvmcontext are little interesting.

If the 'buffer' field of the structure is NULL, the hypercall is a request for
the required buffer size, which written into the 'size' paramater.

If 'buffer' is non NULL, Xen will write to the buffer, and update 'size' with
the amount of data written.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 coregrind/m_syswrap/syswrap-xen.c |   19 +++++++++++++++++++
 include/vki/vki-xen-domctl.h      |    9 ++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/coregrind/m_syswrap/syswrap-xen.c b/coregrind/m_syswrap/syswrap-xen.c
index f99b1ab..f5053bb 100644
--- a/coregrind/m_syswrap/syswrap-xen.c
+++ b/coregrind/m_syswrap/syswrap-xen.c
@@ -581,6 +581,15 @@ PRE(domctl)
       PRE_XEN_DOMCTL_READ(createdomain, flags);
       break;
 
+   case VKI_XEN_DOMCTL_gethvmcontext:
+       /* Xen unconditionally reads the 'buffer' pointer */
+       __PRE_XEN_DOMCTL_READ(gethvmcontext, hvmcontext, buffer);
+       /* Xen only consumes 'size' if 'buffer' is non NULL. A NULL
+        * buffer is a request for the required size. */
+       if ( domctl->u.hvmcontext.buffer.p )
+           __PRE_XEN_DOMCTL_READ(gethvmcontext, hvmcontext, size);
+       break;
+
    case VKI_XEN_DOMCTL_max_mem:
       PRE_XEN_DOMCTL_READ(max_mem, max_memkb);
       break;
@@ -1077,6 +1086,16 @@ POST(domctl){
       POST_XEN_DOMCTL_WRITE(getvcpuinfo, cpu);
       break;
 
+   case VKI_XEN_DOMCTL_gethvmcontext:
+       /* Xen unconditionally writes size... */
+       __POST_XEN_DOMCTL_WRITE(gethvmcontext, hvmcontext, size);
+       /* ...but only writes to the buffer if it was non NULL */
+       if ( domctl->u.hvmcontext.buffer.p )
+           POST_MEM_WRITE((Addr)domctl->u.hvmcontext.buffer.p,
+                          sizeof(*domctl->u.hvmcontext.buffer.p)
+                          * domctl->u.hvmcontext.size);
+       break;
+
    case VKI_XEN_DOMCTL_scheduler_op:
       if ( domctl->u.scheduler_op.cmd == VKI_XEN_DOMCTL_SCHEDOP_getinfo ) {
          switch(domctl->u.scheduler_op.sched_id) {
diff --git a/include/vki/vki-xen-domctl.h b/include/vki/vki-xen-domctl.h
index 815e0a7..24191bd 100644
--- a/include/vki/vki-xen-domctl.h
+++ b/include/vki/vki-xen-domctl.h
@@ -243,6 +243,13 @@ struct vki_xen_guest_tsc_info {
 typedef struct vki_xen_guest_tsc_info vki_xen_guest_tsc_info_t;
 DEFINE_VKI_XEN_GUEST_HANDLE(vki_xen_guest_tsc_info_t);
 
+struct vki_xen_domctl_hvmcontext {
+    vki_uint32_t size; /* IN/OUT size of buffer */
+    VKI_XEN_GUEST_HANDLE_64(vki_uint8) buffer; /* IN/OUT */
+};
+typedef struct vki_xen_domctl_hvmcontext vki_xen_domctl_hvmcontext_t;
+DEFINE_VKI_XEN_GUEST_HANDLE(vki_xen_domctl_hvmcontext_t);
+
 struct vki_xen_domctl_tsc_info {
     VKI_XEN_GUEST_HANDLE_64(vki_xen_guest_tsc_info_t) out_info; /* OUT */
     vki_xen_guest_tsc_info_t info; /* IN */
@@ -291,7 +298,7 @@ struct vki_xen_domctl {
         //struct vki_xen_domctl_disable_migrate   disable_migrate;
         struct vki_xen_domctl_tsc_info          tsc_info;
         //struct vki_xen_domctl_real_mode_area    real_mode_area;
-        //struct vki_xen_domctl_hvmcontext        hvmcontext;
+        struct vki_xen_domctl_hvmcontext        hvmcontext;
         //struct vki_xen_domctl_hvmcontext_partial hvmcontext_partial;
         struct vki_xen_domctl_address_size      address_size;
         //struct vki_xen_domctl_sendtrigger       sendtrigger;
-- 
1.7.10.4