Merge tag 'pull-xenfv-stable-20231106' of git://git.infradead.org/users/dwmw2/qemu into staging

Bugfixes for emulated Xen support

Selected bugfixes for mainline and stable, especially to the per-vCPU
local APIC vector delivery mode for event channel notifications, which
was broken in a number of ways.

The xen-block driver has been defaulting to the wrong protocol for x86
guest, and this fixes that — which is technically an incompatible change
but I'm fairly sure nobody relies on the broken behaviour (and in
production I *have* seen guests which rely on the correct behaviour,
which now matches the blkback driver in the Linux kernel).

A handful of other simple fixes for issues which came to light as new
features (qv) were being developed.

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* tag 'pull-xenfv-stable-20231106' of git://git.infradead.org/users/dwmw2/qemu:
  hw/xen: use correct default protocol for xen-block on x86
  hw/xen: take iothread mutex in xen_evtchn_reset_op()
  hw/xen: fix XenStore watch delivery to guest
  hw/xen: don't clear map_track[] in xen_gnttab_reset()
  hw/xen: select kernel mode for per-vCPU event channel upcall vector
  i386/xen: fix per-vCPU upcall vector for Xen emulation
  i386/xen: Don't advertise XENFEAT_supervisor_mode_kernel

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

4 files changed, 19 insertions, 8 deletions

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index a07cd7e..bfa5396 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -115,9 +115,13 @@ static void xen_block_connect(XenDevice *xendev, Error **errp)
         return;
     }
 
-    if (xen_device_frontend_scanf(xendev, "protocol", "%ms",
-                                  &str) != 1) {
-        protocol = BLKIF_PROTOCOL_NATIVE;
+    if (xen_device_frontend_scanf(xendev, "protocol", "%ms", &str) != 1) {
+        /* x86 defaults to the 32-bit protocol even for 64-bit guests. */
+        if (object_dynamic_cast(OBJECT(qdev_get_machine()), "x86-machine")) {
+            protocol = BLKIF_PROTOCOL_X86_32;
+        } else {
+            protocol = BLKIF_PROTOCOL_NATIVE;
+        }
     } else {
         if (strcmp(str, XEN_IO_PROTO_ABI_X86_32) == 0) {
             protocol = BLKIF_PROTOCOL_X86_32;
diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index a731738..b2b4be9 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -490,6 +490,12 @@ int xen_evtchn_set_callback_param(uint64_t param)
         break;
     }
 
+    /* If the guest has set a per-vCPU callback vector, prefer that. */
+    if (gsi && kvm_xen_has_vcpu_callback_vector()) {
+        in_kernel = kvm_xen_has_cap(EVTCHN_SEND);
+        gsi = 0;
+    }
+
     if (!ret) {
         /* If vector delivery was turned *off* then tell the kernel */
         if ((s->callback_param >> CALLBACK_VIA_TYPE_SHIFT) ==
@@ -1129,6 +1135,7 @@ int xen_evtchn_reset_op(struct evtchn_reset *reset)
         return -ESRCH;
     }
 
+    QEMU_IOTHREAD_LOCK_GUARD();
     return xen_evtchn_soft_reset();
 }
 
diff --git a/hw/i386/kvm/xen_gnttab.c b/hw/i386/kvm/xen_gnttab.c
index 21c30e3..839ec92 100644
--- a/hw/i386/kvm/xen_gnttab.c
+++ b/hw/i386/kvm/xen_gnttab.c
@@ -541,7 +541,5 @@ int xen_gnttab_reset(void)
     s->entries.v1[GNTTAB_RESERVED_XENSTORE].flags = GTF_permit_access;
     s->entries.v1[GNTTAB_RESERVED_XENSTORE].frame = XEN_SPECIAL_PFN(XENSTORE);
 
-    memset(s->map_track, 0, s->max_frames * ENTRIES_PER_FRAME_V1);
-
     return 0;
 }
diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index 660d0b7..8e716a7 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -1357,10 +1357,12 @@ static void fire_watch_cb(void *opaque, const char *path, const char *token)
     } else {
         deliver_watch(s, path, token);
         /*
-         * If the message was queued because there was already ring activity,
-         * no need to wake the guest. But if not, we need to send the evtchn.
+         * Attempt to queue the message into the actual ring, and send
+         * the event channel notification if any bytes are copied.
          */
-        xen_be_evtchn_notify(s->eh, s->be_port);
+        if (s->rsp_pending && put_rsp(s) > 0) {
+            xen_be_evtchn_notify(s->eh, s->be_port);
+        }
     }
 }