xen/pt: allow QEMU to request MSI unmasking at bind time

When a MSI interrupt is bound to a guest using
xc_domain_update_msi_irq (XEN_DOMCTL_bind_pt_irq) the interrupt is
left masked by default.

This causes problems with guests that first configure interrupts and
clean the per-entry MSIX table mask bit and afterwards enable MSIX
globally. In such scenario the Xen internal msixtbl handlers would not
detect the unmasking of MSIX entries because vectors are not yet
registered since MSIX is not enabled, and vectors would be left
masked.

Introduce a new flag in the gflags field to signal Xen whether a MSI
interrupt should be unmasked after being bound.

This also requires to track the mask register for MSI interrupts, so
QEMU can also notify to Xen whether the MSI interrupt should be bound
masked or unmasked

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reported-by: Andreas Kinzler <hfp@posteo.de>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

1 files changed, 10 insertions, 3 deletions

diff --git a/hw/xen/xen_pt_msi.c b/hw/xen/xen_pt_msi.c
index ff9a79f5d2..6d1e3bdeb4 100644
--- a/hw/xen/xen_pt_msi.c
+++ b/hw/xen/xen_pt_msi.c
@@ -24,6 +24,7 @@
 #define XEN_PT_GFLAGS_SHIFT_DM             9
 #define XEN_PT_GFLAGSSHIFT_DELIV_MODE     12
 #define XEN_PT_GFLAGSSHIFT_TRG_MODE       15
+#define XEN_PT_GFLAGSSHIFT_UNMASKED       16
 
 #define latch(fld) latch[PCI_MSIX_ENTRY_##fld / sizeof(uint32_t)]
 
@@ -155,7 +156,8 @@ static int msi_msix_update(XenPCIPassthroughState *s,
                            int pirq,
                            bool is_msix,
                            int msix_entry,
-                           int *old_pirq)
+                           int *old_pirq,
+                           bool masked)
 {
     PCIDevice *d = &s->dev;
     uint8_t gvec = msi_vector(data);
@@ -171,6 +173,8 @@ static int msi_msix_update(XenPCIPassthroughState *s,
         table_addr = s->msix->mmio_base_addr;
     }
 
+    gflags |= masked ? 0 : (1u << XEN_PT_GFLAGSSHIFT_UNMASKED);
+
     rc = xc_domain_update_msi_irq(xen_xc, xen_domid, gvec,
                                   pirq, gflags, table_addr);
 
@@ -273,8 +277,10 @@ int xen_pt_msi_setup(XenPCIPassthroughState *s)
 int xen_pt_msi_update(XenPCIPassthroughState *s)
 {
     XenPTMSI *msi = s->msi;
+
+    /* Current MSI emulation in QEMU only supports 1 vector */
     return msi_msix_update(s, msi_addr64(msi), msi->data, msi->pirq,
-                           false, 0, &msi->pirq);
+                           false, 0, &msi->pirq, msi->mask & 1);
 }
 
 void xen_pt_msi_disable(XenPCIPassthroughState *s)
@@ -355,7 +361,8 @@ static int xen_pt_msix_update_one(XenPCIPassthroughState *s, int entry_nr,
     }
 
     rc = msi_msix_update(s, entry->addr, entry->data, pirq, true,
-                         entry_nr, &entry->pirq);
+                         entry_nr, &entry->pirq,
+                         vec_ctrl & PCI_MSIX_ENTRY_CTRL_MASKBIT);
 
     if (!rc) {
         entry->updated = false;