[xen staging] vpci: Hide extended capability when it fails to initialize

[patchbot@xxxxxxx]

commit 0ba439b9424e6bf4b8da99f03d73d839e8d786bf
Author:     Jiqian Chen <Jiqian.Chen@xxxxxxx>
AuthorDate: Wed Jul 30 13:44:35 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jul 30 13:44:35 2025 +0200

    vpci: Hide extended capability when it fails to initialize
    
    When vpci fails to initialize an extended capability of device, it
    just returns an error and vPCI gets disabled for the whole device.
    
    So, add function to hide extended capability when initialization
    fails. And remove the failed extended capability handler from vpci
    extended capability list.
    
    Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/drivers/vpci/vpci.c    | 88 ++++++++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/pci_regs.h |  5 ++-
 2 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
index da67226e4f..fd02718b47 100644
--- a/xen/drivers/vpci/vpci.c
+++ b/xen/drivers/vpci/vpci.c
@@ -165,6 +165,92 @@ static int vpci_capability_hide(const struct pci_dev 
*pdev, unsigned int cap)
     return 0;
 }
 
+static struct vpci_register *vpci_get_previous_ext_cap_register(
+    const struct vpci *vpci, unsigned int offset)
+{
+    unsigned int pos = PCI_CFG_SPACE_SIZE;
+    struct vpci_register *r;
+
+    if ( offset <= PCI_CFG_SPACE_SIZE )
+    {
+        ASSERT_UNREACHABLE();
+        return NULL;
+    }
+
+    for ( r = vpci_get_register(vpci, pos, 4); r;
+          r = pos > PCI_CFG_SPACE_SIZE ? vpci_get_register(vpci, pos, 4)
+                                       : NULL )
+    {
+        uint32_t header = (uint32_t)(uintptr_t)r->private;
+
+        ASSERT(header == (uintptr_t)r->private);
+
+        pos = PCI_EXT_CAP_NEXT(header);
+        if ( pos == offset )
+            break;
+    }
+
+    return r;
+}
+
+static int vpci_ext_capability_hide(
+    const struct pci_dev *pdev, unsigned int cap)
+{
+    const unsigned int offset = pci_find_ext_capability(pdev->sbdf, cap);
+    struct vpci_register *r, *prev_r;
+    struct vpci *vpci = pdev->vpci;
+    uint32_t header, pre_header;
+
+    if ( offset < PCI_CFG_SPACE_SIZE )
+    {
+        ASSERT_UNREACHABLE();
+        return 0;
+    }
+
+    spin_lock(&vpci->lock);
+    r = vpci_get_register(vpci, offset, 4);
+    if ( !r )
+    {
+        spin_unlock(&vpci->lock);
+        return -ENODEV;
+    }
+
+    header = (uint32_t)(uintptr_t)r->private;
+    if ( offset == PCI_CFG_SPACE_SIZE )
+    {
+        if ( PCI_EXT_CAP_NEXT(header) <= PCI_CFG_SPACE_SIZE )
+            r->private = (void *)0;
+        else
+            /*
+             * The first extended capability (0x100) can not be removed from
+             * the linked list, so instead mask its capability ID to return 0
+             * hopefully forcing OSes to skip it.
+             */
+            r->private = (void *)(uintptr_t)(header & ~PCI_EXT_CAP_ID(header));
+
+        spin_unlock(&vpci->lock);
+        return 0;
+    }
+
+    prev_r = vpci_get_previous_ext_cap_register(vpci, offset);
+    if ( !prev_r )
+    {
+        spin_unlock(&vpci->lock);
+        return -ENODEV;
+    }
+
+    pre_header = (uint32_t)(uintptr_t)prev_r->private;
+    pre_header &= ~PCI_EXT_CAP_NEXT_MASK;
+    pre_header |= header & PCI_EXT_CAP_NEXT_MASK;
+    prev_r->private = (void *)(uintptr_t)pre_header;
+
+    list_del(&r->node);
+    spin_unlock(&vpci->lock);
+    xfree(r);
+
+    return 0;
+}
+
 static int vpci_init_capabilities(struct pci_dev *pdev)
 {
     for ( unsigned int i = 0; i < NUM_VPCI_INIT; i++ )
@@ -206,6 +292,8 @@ static int vpci_init_capabilities(struct pci_dev *pdev)
 
             if ( !is_ext )
                 rc = vpci_capability_hide(pdev, cap);
+            else
+                rc = vpci_ext_capability_hide(pdev, cap);
             if ( rc )
             {
                 printk(XENLOG_ERR "%pd %pp: hide %s cap %u fail rc=%d\n",
diff --git a/xen/include/xen/pci_regs.h b/xen/include/xen/pci_regs.h
index 27b4f44eed..3b6963133d 100644
--- a/xen/include/xen/pci_regs.h
+++ b/xen/include/xen/pci_regs.h
@@ -448,7 +448,10 @@
 /* Extended Capabilities (PCI-X 2.0 and Express) */
 #define PCI_EXT_CAP_ID(header)         ((header) & 0x0000ffff)
 #define PCI_EXT_CAP_VER(header)                (((header) >> 16) & 0xf)
-#define PCI_EXT_CAP_NEXT(header)       (((header) >> 20) & 0xffc)
+#define PCI_EXT_CAP_NEXT_MASK          0xfff00000U
+/* Bottom two bits of next capability position are reserved. */
+#define PCI_EXT_CAP_NEXT(header) \
+    (MASK_EXTR(header, PCI_EXT_CAP_NEXT_MASK) & 0xffcU)
 
 #define PCI_EXT_CAP_ID_ERR     1
 #define PCI_EXT_CAP_ID_VC      2
--
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