xen/vpci: header: filter PCI capabilities

Currently, Xen vPCI only supports virtualizing the MSI and MSI-X capabilities.
Hide all other PCI capabilities (including extended capabilities) from domUs for
now, even though there may be certain devices/drivers that depend on being able
to discover certain capabilities.

We parse the physical PCI capabilities linked list and add vPCI register
handlers for the next elements, inserting our own next value, thus presenting a
modified linked list to the domU.

Introduce helper functions vpci_hw_read8 and vpci_read_val. The vpci_read_val
helper function returns a fixed value, which may be used for read as zero
registers, or registers whose value doesn't change.

Introduce pci_find_next_cap_ttl() helper while adapting the logic from
pci_find_next_cap() to suit our needs, and implement the existing
pci_find_next_cap() in terms of the new helper.

Rename init_bars() to init_header() since it is now doing more than initializing
BARs.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/pci/pci.c

@@ -39,31 +39,42 @@ unsigned int pci_find_cap_offset(pci_sbdf_t sbdf, unsigned int cap)
     return 0;
 }
 
-unsigned int pci_find_next_cap(pci_sbdf_t sbdf, unsigned int pos,
-                               unsigned int cap)
+unsigned int pci_find_next_cap_ttl(pci_sbdf_t sbdf, unsigned int pos,
+                                   const unsigned int caps[], unsigned int n,
+                                   unsigned int *ttl)
 {
-    u8 id;
-    int ttl = 48;
-
-    while ( ttl-- )
+    while ( (*ttl)-- )
     {
+        unsigned int id, i;
+
         pos = pci_conf_read8(sbdf, pos);
         if ( pos < 0x40 )
             break;
 
-        pos &= ~3;
-        id = pci_conf_read8(sbdf, pos + PCI_CAP_LIST_ID);
+        id = pci_conf_read8(sbdf, (pos & ~3) + PCI_CAP_LIST_ID);
 
         if ( id == 0xff )
             break;
-        if ( id == cap )
-            return pos;
+        for ( i = 0; i < n; i++ )
+        {
+            if ( id == caps[i] )
+                return pos;
+        }
 
-        pos += PCI_CAP_LIST_NEXT;
+        pos = (pos & ~3) + PCI_CAP_LIST_NEXT;
     }
+
     return 0;
 }
 
+unsigned int pci_find_next_cap(pci_sbdf_t sbdf, unsigned int pos,
+                               unsigned int cap)
+{
+    unsigned int ttl = 48;
+
+    return pci_find_next_cap_ttl(sbdf, pos, &cap, 1, &ttl) & ~3;
+}
+
 /**
  * pci_find_ext_capability - Find an extended capability
  * @sbdf: PCI device to query

xen/drivers/vpci/header.c

@@ -18,6 +18,7 @@
  */
 
 #include <xen/iocap.h>
+#include <xen/lib.h>
 #include <xen/sched.h>
 #include <xen/softirq.h>
 #include <xen/vpci.h>
@@ -513,7 +514,7 @@ static void cf_check rom_write(
         rom->addr = val & PCI_ROM_ADDRESS_MASK;
 }
 
-static int cf_check init_bars(struct pci_dev *pdev)
+static int cf_check init_header(struct pci_dev *pdev)
 {
     uint16_t cmd;
     uint64_t addr, size;
@@ -545,6 +546,68 @@ static int cf_check init_bars(struct pci_dev *pdev)
     if ( rc )
         return rc;
 
+    if ( !is_hardware_domain(pdev->domain) )
+    {
+        if ( pci_conf_read16(pdev->sbdf, PCI_STATUS) & PCI_STATUS_CAP_LIST )
+        {
+            /* Only expose capabilities to the guest that vPCI can handle. */
+            unsigned int next, ttl = 48;
+            static const unsigned int supported_caps[] = {
+                PCI_CAP_ID_MSI,
+                PCI_CAP_ID_MSIX,
+            };
+
+            next = pci_find_next_cap_ttl(pdev->sbdf, PCI_CAPABILITY_LIST,
+                                         supported_caps,
+                                         ARRAY_SIZE(supported_caps), &ttl);
+
+            rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,
+                                   PCI_CAPABILITY_LIST, 1,
+                                   (void *)(uintptr_t)next);
+            if ( rc )
+                return rc;
+
+            next &= ~3;
+
+            if ( !next )
+                /*
+                 * If we don't have any supported capabilities to expose to the
+                 * guest, mask the PCI_STATUS_CAP_LIST bit in the status
+                 * register.
+                 */
+                mask_cap_list = true;
+
+            while ( next && ttl )
+            {
+                unsigned int pos = next;
+
+                next = pci_find_next_cap_ttl(pdev->sbdf,
+                                             pos + PCI_CAP_LIST_NEXT,
+                                             supported_caps,
+                                             ARRAY_SIZE(supported_caps), &ttl);
+
+                rc = vpci_add_register(pdev->vpci, vpci_hw_read8, NULL,
+                                       pos + PCI_CAP_LIST_ID, 1, NULL);
+                if ( rc )
+                    return rc;
+
+                rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,
+                                       pos + PCI_CAP_LIST_NEXT, 1,
+                                       (void *)(uintptr_t)next);
+                if ( rc )
+                    return rc;
+
+                next &= ~3;
+            }
+        }
+
+        /* Extended capabilities read as zero, write ignore */
+        rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL, 0x100, 4,
+                               (void *)0);
+        if ( rc )
+            return rc;
+    }
+
     /* Utilize rsvdp_mask to hide PCI_STATUS_CAP_LIST from the guest. */
     rc = vpci_add_register_mask(pdev->vpci, vpci_hw_read16, vpci_hw_write16,
                                 PCI_STATUS, 2, NULL,
@@ -642,7 +705,7 @@ static int cf_check init_bars(struct pci_dev *pdev)
 
     return (cmd & PCI_COMMAND_MEMORY) ? modify_bars(pdev, cmd, false) : 0;
 }
-REGISTER_VPCI_INIT(init_bars, VPCI_PRIORITY_MIDDLE);
+REGISTER_VPCI_INIT(init_header, VPCI_PRIORITY_MIDDLE);
 
 /*
  * Local variables:

xen/drivers/vpci/vpci.c

@@ -137,6 +137,18 @@ static void cf_check vpci_ignored_write(
 {
 }
 
+uint32_t cf_check vpci_read_val(
+    const struct pci_dev *pdev, unsigned int reg, void *data)
+{
+    return (uintptr_t)data;
+}
+
+uint32_t cf_check vpci_hw_read8(
+    const struct pci_dev *pdev, unsigned int reg, void *data)
+{
+    return pci_conf_read8(pdev->sbdf, reg);
+}
+
 uint32_t cf_check vpci_hw_read16(
     const struct pci_dev *pdev, unsigned int reg, void *data)
 {

xen/include/xen/pci.h

@@ -205,6 +205,9 @@ int pci_mmcfg_read(unsigned int seg, unsigned int bus,
 int pci_mmcfg_write(unsigned int seg, unsigned int bus,
                     unsigned int devfn, int reg, int len, u32 value);
 unsigned int pci_find_cap_offset(pci_sbdf_t sbdf, unsigned int cap);
+unsigned int pci_find_next_cap_ttl(pci_sbdf_t sbdf, unsigned int pos,
+                                   const unsigned int caps[], unsigned int n,
+                                   unsigned int *ttl);
 unsigned int pci_find_next_cap(pci_sbdf_t sbdf, unsigned int pos,
                                unsigned int cap);
 unsigned int pci_find_ext_capability(pci_sbdf_t sbdf, unsigned int cap);

xen/include/xen/vpci.h

@@ -57,7 +57,13 @@ uint32_t vpci_read(pci_sbdf_t sbdf, unsigned int reg, unsigned int size);
 void vpci_write(pci_sbdf_t sbdf, unsigned int reg, unsigned int size,
                 uint32_t data);
 
+/* Helper to return the value passed in data. */
+uint32_t cf_check vpci_read_val(
+    const struct pci_dev *pdev, unsigned int reg, void *data);
+
 /* Passthrough handlers. */
+uint32_t cf_check vpci_hw_read8(
+    const struct pci_dev *pdev, unsigned int reg, void *data);
 uint32_t cf_check vpci_hw_read16(
     const struct pci_dev *pdev, unsigned int reg, void *data);
 uint32_t cf_check vpci_hw_read32(