hw/pci: Add helper to insert PCIe extended capability at a fixed offset

Add pcie_insert_capability(), a helper to insert a PCIe extended
capability into an existing extended capability list at a caller
specified offset.

Unlike pcie_add_capability(), which always appends a capability to the
end of the list, this helper preserves the existing list ordering while
allowing insertion at an arbitrary offset.

The helper only validates that the insertion does not overwrite an
existing PCIe extended capability header, since corrupting a header
would break the extended capability linked list. Validation of overlaps
with other configuration space registers or capability-specific
register blocks is left to the caller.

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Message-id: 20260126104342.253965-35-skolothumtho@nvidia.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index b302de64191b20918ca6398ce2adebaad7fd06a0..aa9024e532609485494da7313b51d0fb0e2fef42 100644 (file)
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -1050,6 +1050,75 @@ static void pcie_ext_cap_set_next(PCIDevice *dev, uint16_t pos, uint16_t next)
     pci_set_long(dev->config + pos, header);
 }
 
+/*
+ * Insert a PCIe extended capability at a given offset.
+ *
+ * This helper only validates that the insertion does not overwrite an
+ * existing PCIe extended capability header, as corrupting a header would
+ * break the extended capability linked list.
+ *
+ * The caller must ensure that (offset, size) does not overlap with other
+ * registers or capability-specific register blocks. Overlaps with
+ * capability-specific registers are not checked and are considered a
+ * user-controlled override.
+ *
+ * Note: Best effort helper. The PCIe spec does not require extended
+ * capabilities to be ordered, but most devices use a forward-linked list.
+ * Devices that do not consistently use a forward-linked list may cause
+ * insertion to fail.
+ */
+bool pcie_insert_capability(PCIDevice *dev, uint16_t cap_id, uint8_t cap_ver,
+                            uint16_t offset, uint16_t size)
+{
+    uint16_t pos = PCI_CONFIG_SPACE_SIZE, prev = 0;
+    uint32_t header;
+
+    assert(pci_is_express(dev));
+
+    if (!QEMU_IS_ALIGNED(offset, PCI_EXT_CAP_ALIGN) ||
+        size < 8 ||
+        offset < PCI_CONFIG_SPACE_SIZE ||
+        offset >= PCIE_CONFIG_SPACE_SIZE ||
+        offset + size > PCIE_CONFIG_SPACE_SIZE) {
+        return false;
+    }
+
+    header = pci_get_long(dev->config + pos);
+    if (!header) {
+        /* No extended capability present, insertion must be at the ECAP head */
+        if (offset != pos) {
+            return false;
+        }
+        pci_set_long(dev->config + pos, PCI_EXT_CAP(cap_id, cap_ver, 0));
+        goto out;
+    }
+
+    while (header && pos && offset >= pos) {
+        uint16_t next = PCI_EXT_CAP_NEXT(header);
+
+        /* Reject insertion inside an existing ECAP header (4 bytes) */
+        if (offset < pos + PCI_EXT_CAP_ALIGN) {
+            return false;
+        }
+
+        prev = pos;
+        pos = next;
+        header = pos ? pci_get_long(dev->config + pos) : 0;
+    }
+
+    pci_set_long(dev->config + offset, PCI_EXT_CAP(cap_id, cap_ver, pos));
+    if (prev) {
+        pcie_ext_cap_set_next(dev, prev, offset);
+    }
+
+out:
+    /* Make capability read-only by default */
+    memset(dev->wmask + offset, 0, size);
+    memset(dev->w1cmask + offset, 0, size);
+    /* Check capability by default */
+    memset(dev->cmask + offset, 0xFF, size);
+    return true;
+}
 /*
  * Caller must supply valid (offset, size) such that the range wouldn't
  * overlap with other capability or other registers.

diff --git a/include/hw/pci/pcie.h b/include/hw/pci/pcie.h
index c880ae1e04b27c347b6fdf1e21574b0ae1ccceca..d68bfa62572881950932e5a30561991b7b78883b 100644 (file)
--- a/include/hw/pci/pcie.h
+++ b/include/hw/pci/pcie.h
@@ -133,6 +133,8 @@ uint16_t pcie_find_capability(PCIDevice *dev, uint16_t cap_id);
 void pcie_add_capability(PCIDevice *dev,
                          uint16_t cap_id, uint8_t cap_ver,
                          uint16_t offset, uint16_t size);
+bool pcie_insert_capability(PCIDevice *dev, uint16_t cap_id, uint8_t cap_ver,
+                            uint16_t offset, uint16_t size);
 void pcie_sync_bridge_lnk(PCIDevice *dev);
 
 void pcie_acs_init(PCIDevice *dev, uint16_t offset);