In commit 4f78438b45e2 ("vpci: use per-domain PCI lock to protect vpci
structure") a lock was moved from allocate_and_map_msi_pirq() to the
caller and changed from pcidevs_lock() to read_lock(&d->pci_lock).
However, one call path wasn't updated to reflect the change, leading to
a failed assertion observed under the following conditions:

* PV dom0
* Debug build (CONFIG_DEBUG=y) of Xen
* There is an SR-IOV device in the system with one or more VFs enabled
* Dom0 has loaded the driver for the VF and enabled MSI-X

(XEN) Assertion 'd || pcidevs_locked()' failed at drivers/passthrough/pci.c:535
(XEN) ----[ Xen-4.20-unstable  x86_64  debug=y  Not tainted ]----
...
(XEN) Xen call trace:
(XEN)    [<ffff82d040284da8>] R pci_get_pdev+0x4c/0xab
(XEN)    [<ffff82d040344f5c>] F arch/x86/msi.c#read_pci_mem_bar+0x58/0x272
(XEN)    [<ffff82d04034530e>] F arch/x86/msi.c#msix_capability_init+0x198/0x755
(XEN)    [<ffff82d040345dad>] F arch/x86/msi.c#__pci_enable_msix+0x82/0xe8
(XEN)    [<ffff82d0403463e5>] F pci_enable_msi+0x3f/0x78
(XEN)    [<ffff82d04034be2b>] F map_domain_pirq+0x2a4/0x6dc
(XEN)    [<ffff82d04034d4d5>] F allocate_and_map_msi_pirq+0x103/0x262
(XEN)    [<ffff82d04035da5d>] F physdev_map_pirq+0x210/0x259
(XEN)    [<ffff82d04035e798>] F do_physdev_op+0x9c3/0x1454
(XEN)    [<ffff82d040329475>] F pv_hypercall+0x5ac/0x6af
(XEN)    [<ffff82d0402012d3>] F lstar_enter+0x143/0x150

In read_pci_mem_bar(), the VF obtains the struct pci_dev pointer for its
associated PF to access the vf_rlen array. This array is initialized in
pci_add_device() and is only populated in the associated PF's struct
pci_dev.

Access the vf_rlen array via the link to the PF, and remove the
troublesome call to pci_get_pdev().

Fixes: 4f78438b45e2 ("vpci: use per-domain PCI lock to protect vpci structure")
Reported-by: Teddy Astie <teddy.astie@vates.tech>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
Candidate for backport to 4.19
Patch #1 ("xen/pci: introduce PF<->VF links") is pre-requisite

v7->v8:
* no change

v6->v7:
* turn NULL-check into ASSERT
* adjust commentary in struct pf_info

v5->v6:
* add Jan's R-b

v4->v5:
* split the PF<->VF links to a pre-requisite patch
* pass pci_sbdf_t to read_pci_mem_bar()
* use stdint.h types on changed lines
* re-add NULL check for pf_info in read_pci_mem_bar(), as pf_info could
  be NULL

v3->v4:
* handle case when PF is removed with VFs enabled, then re-added with
  VFs disabled

v2->v3:
* link from VF to PF's struct pci_dev *

v1->v2:
* remove call to pci_get_pdev()
---
 xen/arch/x86/msi.c            | 36 ++++++++++++++++++++---------------
 xen/drivers/passthrough/pci.c |  8 +++++---
 xen/include/xen/pci.h         | 11 ++++++++---
 3 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
index fa724911928e..e2360579deda 100644
--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -663,34 +663,34 @@ static int msi_capability_init(struct pci_dev *dev,
     return 0;
 }
 
-static u64 read_pci_mem_bar(u16 seg, u8 bus, u8 slot, u8 func, u8 bir, int vf)
+static uint64_t read_pci_mem_bar(pci_sbdf_t sbdf, uint8_t bir, int vf,
+                                 const struct pf_info *pf_info)
 {
+    uint16_t seg = sbdf.seg;
+    uint8_t bus = sbdf.bus, slot = sbdf.dev, func = sbdf.fn;
     u8 limit;
     u32 addr, base = PCI_BASE_ADDRESS_0;
     u64 disp = 0;
 
     if ( vf >= 0 )
     {
-        struct pci_dev *pdev = pci_get_pdev(NULL,
-                                            PCI_SBDF(seg, bus, slot, func));
         unsigned int pos;
         uint16_t ctrl, num_vf, offset, stride;
 
-        if ( !pdev )
-            return 0;
+        ASSERT(pf_info);
 
-        pos = pci_find_ext_capability(pdev->sbdf, PCI_EXT_CAP_ID_SRIOV);
-        ctrl = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_CTRL);
-        num_vf = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_NUM_VF);
-        offset = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_VF_OFFSET);
-        stride = pci_conf_read16(pdev->sbdf, pos + PCI_SRIOV_VF_STRIDE);
+        pos = pci_find_ext_capability(sbdf, PCI_EXT_CAP_ID_SRIOV);
+        ctrl = pci_conf_read16(sbdf, pos + PCI_SRIOV_CTRL);
+        num_vf = pci_conf_read16(sbdf, pos + PCI_SRIOV_NUM_VF);
+        offset = pci_conf_read16(sbdf, pos + PCI_SRIOV_VF_OFFSET);
+        stride = pci_conf_read16(sbdf, pos + PCI_SRIOV_VF_STRIDE);
 
         if ( !pos ||
              !(ctrl & PCI_SRIOV_CTRL_VFE) ||
              !(ctrl & PCI_SRIOV_CTRL_MSE) ||
              !num_vf || !offset || (num_vf > 1 && !stride) ||
              bir >= PCI_SRIOV_NUM_BARS ||
-             !pdev->vf_rlen[bir] )
+             !pf_info->vf_rlen[bir] )
             return 0;
         base = pos + PCI_SRIOV_BAR;
         vf -= PCI_BDF(bus, slot, func) + offset;
@@ -704,8 +704,8 @@ static u64 read_pci_mem_bar(u16 seg, u8 bus, u8 slot, u8 func, u8 bir, int vf)
         }
         if ( vf >= num_vf )
             return 0;
-        BUILD_BUG_ON(ARRAY_SIZE(pdev->vf_rlen) != PCI_SRIOV_NUM_BARS);
-        disp = vf * pdev->vf_rlen[bir];
+        BUILD_BUG_ON(ARRAY_SIZE(pf_info->vf_rlen) != PCI_SRIOV_NUM_BARS);
+        disp = vf * pf_info->vf_rlen[bir];
         limit = PCI_SRIOV_NUM_BARS;
     }
     else switch ( pci_conf_read8(PCI_SBDF(seg, bus, slot, func),
@@ -814,6 +814,7 @@ static int msix_capability_init(struct pci_dev *dev,
         int vf;
         paddr_t pba_paddr;
         unsigned int pba_offset;
+        const struct pf_info *pf_info;
 
         if ( !dev->info.is_virtfn )
         {
@@ -821,6 +822,7 @@ static int msix_capability_init(struct pci_dev *dev,
             pslot = slot;
             pfunc = func;
             vf = -1;
+            pf_info = NULL;
         }
         else
         {
@@ -828,9 +830,12 @@ static int msix_capability_init(struct pci_dev *dev,
             pslot = PCI_SLOT(dev->info.physfn.devfn);
             pfunc = PCI_FUNC(dev->info.physfn.devfn);
             vf = dev->sbdf.bdf;
+            ASSERT(dev->pf_pdev);
+            pf_info = &dev->pf_pdev->physfn;
         }
 
-        table_paddr = read_pci_mem_bar(seg, pbus, pslot, pfunc, bir, vf);
+        table_paddr = read_pci_mem_bar(PCI_SBDF(seg, pbus, pslot, pfunc), bir,
+                                       vf, pf_info);
         WARN_ON(msi && msi->table_base != table_paddr);
         if ( !table_paddr )
         {
@@ -853,7 +858,8 @@ static int msix_capability_init(struct pci_dev *dev,
 
         pba_offset = pci_conf_read32(dev->sbdf, msix_pba_offset_reg(pos));
         bir = (u8)(pba_offset & PCI_MSIX_BIRMASK);
-        pba_paddr = read_pci_mem_bar(seg, pbus, pslot, pfunc, bir, vf);
+        pba_paddr = read_pci_mem_bar(PCI_SBDF(seg, pbus, pslot, pfunc), bir, vf,
+                                     pf_info);
         WARN_ON(!pba_paddr);
         pba_paddr += pba_offset & ~PCI_MSIX_BIRMASK;
 
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 3fe2e7884f45..6af1136b6350 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -735,7 +735,7 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
         }
     }
 
-    if ( !pdev->info.is_virtfn && !pdev->vf_rlen[0] )
+    if ( !pdev->info.is_virtfn && !pdev->physfn.vf_rlen[0] )
     {
         unsigned int pos = pci_find_ext_capability(pdev->sbdf,
                                                    PCI_EXT_CAP_ID_SRIOV);
@@ -747,7 +747,9 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
         {
             unsigned int i;
 
-            BUILD_BUG_ON(ARRAY_SIZE(pdev->vf_rlen) != PCI_SRIOV_NUM_BARS);
+            BUILD_BUG_ON(ARRAY_SIZE(pdev->physfn.vf_rlen) !=
+                                    PCI_SRIOV_NUM_BARS);
+
             for ( i = 0; i < PCI_SRIOV_NUM_BARS; )
             {
                 unsigned int idx = pos + PCI_SRIOV_BAR + i * 4;
@@ -762,7 +764,7 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
                     continue;
                 }
                 ret = pci_size_mem_bar(pdev->sbdf, idx, NULL,
-                                       &pdev->vf_rlen[i],
+                                       &pdev->physfn.vf_rlen[i],
                                        PCI_BAR_VF |
                                        ((i == PCI_SRIOV_NUM_BARS - 1) ?
                                         PCI_BAR_LAST : 0));
diff --git a/xen/include/xen/pci.h b/xen/include/xen/pci.h
index 977c0d08f78a..f784e9116059 100644
--- a/xen/include/xen/pci.h
+++ b/xen/include/xen/pci.h
@@ -159,9 +159,14 @@ struct pci_dev {
      * List entry if VF.
      */
     struct list_head vf_list;
-    u64 vf_rlen[6];
-    /* Link from VF to PF. Only populated for VFs. */
-    const struct pci_dev *pf_pdev;
+    union {
+        struct pf_info {
+            /* Only populated for PFs. */
+            uint64_t vf_rlen[PCI_SRIOV_NUM_BARS];
+        } physfn;
+        /* Link from VF to PF. Only populated for VFs. */
+        const struct pci_dev *pf_pdev;
+    };
 
     /* Data for vPCI. */
     struct vpci *vpci;
-- 
2.47.0