ignore writes to some RO registers in PCI config space (#576)

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
Reviewed-by: John Levon <john.levon@nutanix.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/lib/pci.c b/lib/pci.c
index bd3b4d2..27cba28 100644
--- a/lib/pci.c
+++ b/lib/pci.c
@@ -225,11 +225,18 @@ pci_hdr_write(vfu_ctx_t *vfu_ctx, const char *buf, loff_t offset)
         ret = handle_command_write(vfu_ctx, cfg_space, buf);
         break;
     case PCI_STATUS:
+        /* FIXME ignoring write completely is wrong as some bits are RW1C */
         vfu_log(vfu_ctx, LOG_INFO, "write to status ignored");
         break;
-    case PCI_INTERRUPT_PIN:
-        vfu_log(vfu_ctx, LOG_ERR, "attempt to write read-only field IPIN");
-        ret = ERROR_INT(EINVAL);
+    /*
+     * According to the PCI spec, writing to read-only registers must be
+     * ignored by the device. Some OSes tend to do this, e.g. FreeBSD.
+     */
+    case offsetof(vfu_pci_hdr_t, rid):
+    case offsetof(vfu_pci_hdr_t, cc):
+    case offsetof(vfu_pci_hdr_t, intr.ipin):
+    case offsetof(vfu_pci_hdr_t, mgnt):
+    case offsetof(vfu_pci_hdr_t, mlat):
         break;
     case PCI_INTERRUPT_LINE:
         cfg_space->hdr.intr.iline = buf[0];
@@ -347,7 +354,8 @@ pci_config_space_size_for_reg(loff_t offset)
         PCI_REG_SZ(ss),
         PCI_REG_SZ(erom),
         PCI_REG_SZ(cap),
-        PCI_REG_SZ(intr),
+        PCI_REG_SZ(intr.iline),
+        PCI_REG_SZ(intr.ipin),
         PCI_REG_SZ(mgnt),
         PCI_REG_SZ(mlat)
     };