[Xen-changelog] [xen master] domctl: pause vCPU for context reads

[patchbot@xxxxxxx]

commit fee61634e8f3fec7c137f0d16478c64c7f355587
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Feb 6 12:20:48 2014 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 6 12:20:48 2014 +0100

    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@xxxxxxxx>
    Acked-by: Keir Fraser <keir@xxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/arch/x86/domctl.c |    7 +++++++
 xen/common/domctl.c   |   14 +++++---------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 432a180..26635ff 100644
--- 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 f237be4..7cf610a 100644
--- 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) )
--
generated by git-patchbot for /home/xen/git/xen.git#master

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