Re: [PATCH RFC v1 1/3] vfio/pci: detect the support of dynamic MSI-X allocation

[Cédric Le Goater]

Hello Jing,

On 7/27/23 09:24, Jing Liu wrote:

From: Reinette Chatre <reinette.cha...@intel.com>

Kernel provides the guidance of dynamic MSI-X allocation support of
passthrough device, by clearing the VFIO_IRQ_INFO_NORESIZE flag to
guide user space.

Fetch and store the flags from host for later use to determine if
specific flags are set.

Signed-off-by: Reinette Chatre <reinette.cha...@intel.com>
Signed-off-by: Jing Liu <jing2....@intel.com>
---
  hw/vfio/pci.c        | 12 ++++++++++++
  hw/vfio/pci.h        |  1 +
  hw/vfio/trace-events |  2 ++
  3 files changed, 15 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index a205c6b1130f..0c4ac0873d40 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1572,6 +1572,7 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, 
Error **errp)

static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)

  {
+    struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info) };
      int ret;
      Error *err = NULL;

@@ -1624,6 +1625,17 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)

          memory_region_set_enabled(&vdev->pdev.msix_table_mmio, false);
      }

+ irq_info.index = VFIO_PCI_MSIX_IRQ_INDEX;

+    ret = ioctl(vdev->vbasedev.fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
+    if (ret) {
+        /* This can fail for an old kernel or legacy PCI dev */
+        trace_vfio_msix_setup_get_irq_info_failure(strerror(errno));

Is it possible to detect the error reported by a kernel (< 6.4) when
dynamic MSI-X are not supported. Looking at vfio_pci_ioctl_get_irq_info()
in the kernel, could info.flags be tested against VFIO_IRQ_INFO_NORESIZE ?

In that case, QEMU should report an error and the trace event is not
needed.

Thanks,

C.

+    } else {
+        vdev->msix->irq_info_flags = irq_info.flags;
+    }
+    trace_vfio_msix_setup_irq_info_flags(vdev->vbasedev.name,
+                                         vdev->msix->irq_info_flags);
+
      return 0;
  }

diff --git a/hw/vfio/pci.h b/hw/vfio/pci.h

index a2771b9ff3cc..ad34ec56d0ae 100644
--- a/hw/vfio/pci.h
+++ b/hw/vfio/pci.h
@@ -113,6 +113,7 @@ typedef struct VFIOMSIXInfo {
      uint32_t table_offset;
      uint32_t pba_offset;
      unsigned long *pending;
+    uint32_t irq_info_flags;
  } VFIOMSIXInfo;

#define TYPE_VFIO_PCI "vfio-pci"

diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index ee7509e68e4f..7d4a398f044d 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -28,6 +28,8 @@ vfio_pci_read_config(const char *name, int addr, int len, int val) 
" (%s, @0x%x,
  vfio_pci_write_config(const char *name, int addr, int val, int len) " (%s, @0x%x, 
0x%x, len=0x%x)"
  vfio_msi_setup(const char *name, int pos) "%s PCI MSI CAP @0x%x"
  vfio_msix_early_setup(const char *name, int pos, int table_bar, int offset, int 
entries) "%s PCI MSI-X CAP @0x%x, BAR %d, offset 0x%x, entries %d"
+vfio_msix_setup_get_irq_info_failure(const char *errstr) "VFIO_DEVICE_GET_IRQ_INFO 
failure: %s"
+vfio_msix_setup_irq_info_flags(const char *name, uint32_t flags) " (%s) MSI-X irq 
info flags 0x%x"
  vfio_check_pcie_flr(const char *name) "%s Supports FLR via PCIe cap"
  vfio_check_pm_reset(const char *name) "%s Supports PM reset"
  vfio_check_af_flr(const char *name) "%s Supports FLR via AF cap"