Re: [Qemu-devel] [PATCH for v1.0 1/3] msix: track function masked in pci device state

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Dec 04, 2011 at 04:47:17PM -0700, Cam Macdonell wrote:
> On Sun, Dec 4, 2011 at 3:20 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Fri, Dec 02, 2011 at 04:34:21PM -0700, Cam Macdonell wrote:
> >> Based on a git bisect, this patch breaks msi-x interrupt delivery in
> >> the ivshmem device.
> >
> > I think the following should fix it. Compiled-only -
> > could you pls check? If yes let's apply to the stable branch.
> 
> Thanks for the patch Michael.
> 
> It addresses the need for msix_write_config() to be called, but the
> addition of the msix_reset() is causing a reset of the vectors after
> they've been initialized in pci_ivshmem_init().  So, interrupts still
> aren't delivered with this patch applied as it is.
> 
> In particular, a reset occurs after pci_ivshmem_init runs, so the
> msix_entry_used array is reset to 0s, which causes the interrupt
> delivery to fail.
> 
> If I comment out the msix_reset(), then interrupts are delivered.
> Would the reset be caused by a bug in the guest driver?  or do I need
> to reconfigure the msix after reset?  I'm unclear as to the proper
> behaviour after a reset.
> 
> Thanks,
> Cam
> 

I didn't anticipate this, virtio only configures vectors when msi-x is enabled.
For 1.0 it's safest to do the same and just re-enable after reset.

So we'll end up with something like the following - does it help?

Side note: exit(1) is not the best way to handle
errors in the init function. I think you should add error_report, then
goto err on failures to init, cleanup what you have set up
meanwhile and return an error code.

diff --git a/hw/ivshmem.c b/hw/ivshmem.c
index 242fbea..c58f4d3 100644
--- a/hw/ivshmem.c
+++ b/hw/ivshmem.c
@@ -500,11 +500,29 @@ static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
     return;
 }
 
+/* Select the MSI-X vectors used by device.
+ * ivshmem maps events to vectors statically, so
+ * we just enable all vectors on init and after reset. */
+static void ivshmem_use_msix(IVShmemState * s)
+{
+    int i;
+
+    if (!msix_present(&s->dev)) {
+        return;
+    }
+
+    for (i = 0; i < s->vectors; i++) {
+        msix_vector_use(&s->dev, i);
+    }
+}
+
 static void ivshmem_reset(DeviceState *d)
 {
     IVShmemState *s = DO_UPCAST(IVShmemState, dev.qdev, d);
 
     s->intrstatus = 0;
+    msix_reset(&s->dev);
+    ivshmem_use_msix(s);
     return;
 }
 
@@ -535,12 +553,8 @@ static uint64_t ivshmem_get_size(IVShmemState * s) {
     return value;
 }
 
-static void ivshmem_setup_msi(IVShmemState * s) {
-
-    int i;
-
-    /* allocate the MSI-X vectors */
-
+static void ivshmem_setup_msi(IVShmemState * s)
+{
     memory_region_init(&s->msix_bar, "ivshmem-msix", 4096);
     if (!msix_init(&s->dev, s->vectors, &s->msix_bar, 1, 0)) {
         pci_register_bar(&s->dev, 1, PCI_BASE_ADDRESS_SPACE_MEMORY,
@@ -551,13 +565,10 @@ static void ivshmem_setup_msi(IVShmemState * s) {
         exit(1);
     }
 
-    /* 'activate' the vectors */
-    for (i = 0; i < s->vectors; i++) {
-        msix_vector_use(&s->dev, i);
-    }
-
     /* allocate Qemu char devices for receiving interrupts */
     s->eventfd_table = g_malloc0(s->vectors * sizeof(EventfdEntry));
+
+    ivshmem_use_msix(s);
 }
 
 static void ivshmem_save(QEMUFile* f, void *opaque)
@@ -610,6 +621,13 @@ static int ivshmem_load(QEMUFile* f, void *opaque, int version_id)
     return 0;
 }
 
+static void ivshmem_write_config(PCIDevice *pci_dev, uint32_t address,
+				 uint32_t val, int len)
+{
+    pci_default_write_config(pci_dev, address, val, len);
+    msix_write_config(pci_dev, address, val, len);
+}
+
 static int pci_ivshmem_init(PCIDevice *dev)
 {
     IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
@@ -734,6 +752,8 @@ static int pci_ivshmem_init(PCIDevice *dev)
 
     }
 
+    s->dev.config_write = ivshmem_write_config;
+
     return 0;
 }