xen/pt: add a few PCI config space field descriptions

Since the next patch will turn all not explicitly described fields
read-only by default, those fields that have guest writable bits need
to be given explicit descriptors.

This is a preparatory patch for XSA-131.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/hw/pass-through.c
+++ b/hw/pass-through.c
@@ -538,6 +538,16 @@ static struct pt_reg_info_tbl pt_emu_reg
         .u.b.restore  = NULL,
     },
     {
+        .offset     = PCI_VPD_ADDR,
+        .size       = 2,
+        .ro_mask    = 0x0003,
+        .emu_mask   = 0x0003,
+        .init       = pt_common_reg_init,
+        .u.w.read   = pt_word_reg_read,
+        .u.w.write  = pt_word_reg_write,
+        .u.w.restore = pt_word_reg_restore,
+    },
+    {
         .size = 0,
     },
 };
@@ -599,6 +609,17 @@ static struct pt_reg_info_tbl pt_emu_reg
         .u.w.write  = pt_word_reg_write,
         .u.w.restore  = pt_word_reg_restore,
     },
+    /* Device Status reg */
+    {
+        .offset     = PCI_EXP_DEVSTA,
+        .size       = 2,
+        .res_mask   = 0xFFC0,
+        .ro_mask    = 0x0030,
+        .init       = pt_common_reg_init,
+        .u.w.read   = pt_word_reg_read,
+        .u.w.write  = pt_word_reg_write,
+        .u.w.restore  = pt_word_reg_restore,
+    },
     /* Link Control reg */
     {
         .offset     = PCI_EXP_LNKCTL,
@@ -611,6 +632,16 @@ static struct pt_reg_info_tbl pt_emu_reg
         .u.w.write  = pt_word_reg_write,
         .u.w.restore  = pt_word_reg_restore,
     },
+    /* Link Status reg */
+    {
+        .offset     = PCI_EXP_LNKSTA,
+        .size       = 2,
+        .ro_mask    = 0x3FFF,
+        .init       = pt_common_reg_init,
+        .u.w.read   = pt_word_reg_read,
+        .u.w.write  = pt_word_reg_write,
+        .u.w.restore = pt_word_reg_restore,
+    },
     /* Device Control 2 reg */
     {
         .offset     = 0x28,
--- a/hw/pass-through.h
+++ b/hw/pass-through.h
@@ -105,6 +105,14 @@
 #define PCI_EXP_TYPE_ROOT_EC     0xa
 #endif
 
+#ifndef PCI_VPD_ADDR
+/* Vital Product Data */
+#define PCI_VPD_ADDR		2	/* Address to access (15 bits!) */
+#define  PCI_VPD_ADDR_MASK	0x7fff	/* Address mask */
+#define  PCI_VPD_ADDR_F		0x8000	/* Write 0, 1 indicates completion */
+#define PCI_VPD_DATA		4	/* 32-bits of data returned here */
+#endif
+
 #ifndef PCI_ERR_UNCOR_MASK
 /* Uncorrectable Error Mask */
 #define PCI_ERR_UNCOR_MASK      8