[PATCH v4] x86/hvm: Widen condition for is_hvm_pv_evtchn_domain() and report fix in CPUID

[Jane Malalane <jane.malalane@xxxxxxxxxx>]

Have is_hvm_pv_evtchn_domain() return true for vector callbacks for
evtchn delivery set up on a per-vCPU basis via
HVMOP_set_evtchn_upcall_vector.

Assume that if vCPU0 uses HVMOP_set_evtchn_upcall_vector, all
remaining vCPUs will too and thus remove is_hvm_pv_evtchn_vcpu() and
replace sole caller with is_hvm_pv_evtchn_domain().

is_hvm_pv_evtchn_domain() returning true is a condition for setting up
physical IRQ to event channel mappings. Therefore, also add a CPUID
bit so that guests know whether the check in is_hvm_pv_evtchn_domain()
will fail when using HVMOP_set_evtchn_upcall_vector. This matters for
guests that route PIRQs over event channels since
is_hvm_pv_evtchn_domain() is a condition in physdev_map_pirq().

The naming of the CPUID bit is quite generic about upcall support
being available. That's done so that the define name doesn't become
overly long.

A guest that doesn't care about physical interrupts routed over event
channels can just test for the availability of the hypercall directly
(HVMOP_set_evtchn_upcall_vector) without checking the CPUID bit.

Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>
---
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>

v4:
 * Remove is_hvm_pv_evtchn_vcpu and replace sole caller.

v3:
 * Improve commit message and title.

v2:
 * Since the naming of the CPUID bit is quite generic, better explain
   when it should be checked for, in code comments and commit message.
---
 xen/arch/x86/hvm/irq.c              | 2 +-
 xen/arch/x86/include/asm/domain.h   | 9 +++++++--
 xen/arch/x86/traps.c                | 6 ++++++
 xen/include/public/arch-x86/cpuid.h | 5 +++++
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/irq.c b/xen/arch/x86/hvm/irq.c
index 5a7f39b54f..19252448cb 100644
--- a/xen/arch/x86/hvm/irq.c
+++ b/xen/arch/x86/hvm/irq.c
@@ -325,7 +325,7 @@ void hvm_assert_evtchn_irq(struct vcpu *v)
 
         vlapic_set_irq(vcpu_vlapic(v), vector, 0);
     }
-    else if ( is_hvm_pv_evtchn_vcpu(v) )
+    else if ( is_hvm_pv_evtchn_domain(v->domain) )
         vcpu_kick(v);
     else if ( v->vcpu_id == 0 )
         hvm_set_callback_irq_level(v);
diff --git a/xen/arch/x86/include/asm/domain.h 
b/xen/arch/x86/include/asm/domain.h
index 35898d725f..dcd221cc6f 100644
--- a/xen/arch/x86/include/asm/domain.h
+++ b/xen/arch/x86/include/asm/domain.h
@@ -14,9 +14,14 @@
 
 #define has_32bit_shinfo(d)    ((d)->arch.has_32bit_shinfo)
 
+/*
+ * Set to true if either the global vector-type callback or per-vCPU
+ * LAPIC vectors are used. Assume all vCPUs will use
+ * HVMOP_set_evtchn_upcall_vector as long as the initial vCPU does.
+ */
 #define is_hvm_pv_evtchn_domain(d) (is_hvm_domain(d) && \
-        (d)->arch.hvm.irq->callback_via_type == HVMIRQ_callback_vector)
-#define is_hvm_pv_evtchn_vcpu(v) (is_hvm_pv_evtchn_domain(v->domain))
+        ((d)->arch.hvm.irq->callback_via_type == HVMIRQ_callback_vector || \
+         (d)->vcpu[0]->arch.hvm.evtchn_upcall_vector))
 #define is_domain_direct_mapped(d) ((void)(d), 0)
 
 #define VCPU_TRAP_NONE         0
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 25bffe47d7..1a7f9df067 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1152,6 +1152,12 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, 
uint32_t leaf,
         res->a |= XEN_HVM_CPUID_DOMID_PRESENT;
         res->c = d->domain_id;
 
+        /*
+         * Per-vCPU event channel upcalls are implemented and work
+         * correctly with PIRQs routed over event channels.
+         */
+        res->a |= XEN_HVM_CPUID_UPCALL_VECTOR;
+
         break;
 
     case 5: /* PV-specific parameters */
diff --git a/xen/include/public/arch-x86/cpuid.h 
b/xen/include/public/arch-x86/cpuid.h
index f2b2b3632c..c49eefeaf8 100644
--- a/xen/include/public/arch-x86/cpuid.h
+++ b/xen/include/public/arch-x86/cpuid.h
@@ -109,6 +109,11 @@
  * field from 8 to 15 bits, allowing to target APIC IDs up 32768.
  */
 #define XEN_HVM_CPUID_EXT_DEST_ID      (1u << 5)
+/*
+ * Per-vCPU event channel upcalls work correctly with physical IRQs
+ * bound to event channels.
+ */
+#define XEN_HVM_CPUID_UPCALL_VECTOR    (1u << 6)
 
 /*
  * Leaf 6 (0x40000x05)
-- 
2.11.0