From 3d4ce135ea3b396bb63752c39e6234366d590c16 Mon Sep 17 00:00:00 2001 From: George Dunlap Date: Mon, 22 May 2017 11:38:31 +0100 Subject: [PATCH] Restore HVM_OP hypercall continuation (partial revert of ae20ccf) Commit ae20ccf removed the hypercall continuation logic from the end of do_hvm_op(), claiming: "This patch removes the need for handling HVMOP restarts, so that infrastructure is removed." That turns out to be false. The removal of HVMOP_set_mem_type removed the need to store a start iteration value in the hypercall continuation, but a grep through hvm.c for ERESTART turns up at least two places where do_hvm_op() may still need a hypercall continuation: * HVMOP_set_hvm_param can return -ERESTART when setting HVM_PARAM_IDENT_PT in the event that it fails to acquire the domctl lock * HVMOP_flush_tlbs can return -ERESTART if several vcpus call it at the same time In both cases, a simple restart (with no stored iteration information) is necessary. Add a check for -ERESTART again, along with a comment at the top of the function regarding the lack of decoding any information from the op value. Reported-by: Xudong Hao Signed-off-by: George Dunlap --- CC: Andrew Cooper CC: Jan Beulich CC: Paul Durrant --- xen/arch/x86/hvm/hvm.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 81691e2..e3e817d 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -4544,6 +4544,13 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg) { long rc = 0; + /* + * NB: hvm_op can be part of a restarted hypercall; but at the + * moment the only hypercalls which do continuations don't need to + * store any iteration information (since they're just re-trying + * the acquisition of a lock). + */ + switch ( op ) { case HVMOP_set_evtchn_upcall_vector: @@ -4636,6 +4643,10 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg) } } + if ( rc == -ERESTART ) + rc = hypercall_create_continuation(__HYPERVISOR_hvm_op, "lh", + op, arg); + return rc; } @@ -4869,4 +4880,3 @@ void hvm_set_segment_register(struct vcpu *v, enum x86_segment seg, * indent-tabs-mode: nil * End: */ - -- 2.1.4