domctl: pause vCPU for context reads

"Base" context reads already paused the subject vCPU when being the
current one, but that special case isn't being properly dealt with
anyway (at the very least when x86's fsgsbase feature is in use), so
just disallow it.

"Extended" context reads so far didn't do any pausing.

While we can't avoid the reported data being stale by the time it
arrives at the caller, this way we at least guarantee that it is
consistent.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 432a180865860a5274ea6c798b34dac9037c50a8..26635ffc47945bbe2ab3b437b5bf2c742e90ad02 100644 (file)
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -819,7 +819,13 @@ long arch_do_domctl(
 
         if ( domctl->cmd == XEN_DOMCTL_get_ext_vcpucontext )
         {
+            if ( v == current ) /* no vcpu_pause() */
+                break;
+
             evc->size = sizeof(*evc);
+
+            vcpu_pause(v);
+
             if ( is_pv_domain(d) )
             {
                 evc->sysenter_callback_cs      =
@@ -849,6 +855,7 @@ long arch_do_domctl(
             evc->vmce.mci_ctl2_bank1 = v->arch.vmce.bank[1].mci_ctl2;
 
             ret = 0;
+            vcpu_unpause(v);
             copyback = 1;
         }
         else

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index f237be4a7712824f0143277082f23112ef074152..7cf610a4613b25ab3c2d601fb1a2cd02e0e5a177 100644 (file)
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -675,11 +675,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         struct vcpu         *v;
 
         ret = -EINVAL;
-        if ( op->u.vcpucontext.vcpu >= d->max_vcpus )
-            goto getvcpucontext_out;
-
-        ret = -ESRCH;
-        if ( (v = d->vcpu[op->u.vcpucontext.vcpu]) == NULL )
+        if ( op->u.vcpucontext.vcpu >= d->max_vcpus ||
+             (v = d->vcpu[op->u.vcpucontext.vcpu]) == NULL ||
+             v == current ) /* no vcpu_pause() */
             goto getvcpucontext_out;
 
         ret = -ENODATA;
@@ -694,14 +692,12 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         if ( (c.nat = xmalloc(struct vcpu_guest_context)) == NULL )
             goto getvcpucontext_out;
 
-        if ( v != current )
-            vcpu_pause(v);
+        vcpu_pause(v);
 
         arch_get_info_guest(v, c);
         ret = 0;
 
-        if ( v != current )
-            vcpu_unpause(v);
+        vcpu_unpause(v);
 
 #ifdef CONFIG_COMPAT
         if ( !is_pv_32on64_vcpu(v) )