[Xen-changelog] [xen stable-4.5] x86/hvm: wait for at least one ioreq server to be enabled

[patchbot@xxxxxxx]

commit 2bfef90c47de6ff89c01cafe3e0c413ee223700b
Author:     Paul Durrant <paul.durrant@xxxxxxxxxx>
AuthorDate: Wed Feb 18 16:39:46 2015 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 18 16:39:46 2015 +0100

    x86/hvm: wait for at least one ioreq server to be enabled
    
    In the case where a stub domain is providing emulation for an HVM
    guest, there is no interlock in the toolstack to make sure that
    the stub domain is up and running before the guest is unpaused.
    
    Prior to the introduction of ioreq servers this was not a problem,
    since there was only ever one emulator so ioreqs were simply
    created anyway and the vcpu remained blocked until the stub domain
    started and picked up the ioreq.
    
    Since ioreq servers allow for multiple emulators for a single guest
    it's not possible to know a priori which emulator will handle a
    particular ioreq, so emulators must attach to a guest before the
    guest runs.
    
    This patch works around the lack of interlock in the toolstack for
    stub domains by keeping the domain paused until at least one ioreq
    server is created and enabled, which in practice means the stub
    domain is indeed up and running.
    
    Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    master commit: dd748d128d86996592afafea02e578cc7d4e6d42
    master date: 2015-02-10 13:28:40 +0100
---
 xen/arch/x86/hvm/hvm.c           |   21 +++++++++++++++++++++
 xen/include/asm-x86/hvm/domain.h |    1 +
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 72be5b9..5bf8c3d 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -874,6 +874,13 @@ static void hvm_ioreq_server_enable(struct 
hvm_ioreq_server *s,
 
   done:
     spin_unlock(&s->lock);
+
+    /* This check is protected by the domain ioreq server lock. */
+    if ( d->arch.hvm_domain.ioreq_server.waiting )
+    {
+        d->arch.hvm_domain.ioreq_server.waiting = 0;
+        domain_unpause(d);
+    }
 }
 
 static void hvm_ioreq_server_disable(struct hvm_ioreq_server *s,
@@ -1424,6 +1431,20 @@ int hvm_domain_initialise(struct domain *d)
 
     spin_lock_init(&d->arch.hvm_domain.ioreq_server.lock);
     INIT_LIST_HEAD(&d->arch.hvm_domain.ioreq_server.list);
+    
+    /*
+     * In the case where a stub domain is providing emulation for
+     * the guest, there is no interlock in the toolstack to prevent
+     * the guest from running before the stub domain is ready.
+     * Hence the domain must remain paused until at least one ioreq
+     * server is created and enabled.
+     */
+    if ( !is_pvh_domain(d) )
+    {
+        domain_pause(d);
+        d->arch.hvm_domain.ioreq_server.waiting = 1;
+    }
+
     spin_lock_init(&d->arch.hvm_domain.irq_lock);
     spin_lock_init(&d->arch.hvm_domain.uc_lock);
 
diff --git a/xen/include/asm-x86/hvm/domain.h b/xen/include/asm-x86/hvm/domain.h
index 2757c7f..0702bf5 100644
--- a/xen/include/asm-x86/hvm/domain.h
+++ b/xen/include/asm-x86/hvm/domain.h
@@ -83,6 +83,7 @@ struct hvm_domain {
     struct {
         spinlock_t       lock;
         ioservid_t       id;
+        bool_t           waiting;
         struct list_head list;
     } ioreq_server;
     struct hvm_ioreq_server *default_ioreq_server;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.5

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