[Qemu-devel] [PATCH] pcie: fix link active status bit migration

[Qemu-devel] [PATCH] pcie: fix link active status bit migration

[Michael S. Tsirkin]

We changed link status register in pci express endpoint capability
over time. Specifically,

commit b2101eae63ea57b571cee4a9075a4287d24ba4a4 ("pcie: Set the "link
active" in the link status register") set data link layer link active
bit in this register without adding compatibility to old machine types.

When migrating from qemu 2.3 and older this affects xhci devices which
under machine type 2.0 and older have a pci express endpoint capability
even if they are on a pci bus.

Add compatibility flags to make this bit value match what it was under
2.3.

Additionally, to avoid breaking migration from qemu 2.3 and up,
suppress checking link status during migration: this seems sane
since hardware can change link status at any time.

https://bugzilla.redhat.com/show_bug.cgi?id=1352860

Reported-by: Gerd Hoffmann <kraxel@redhat.com>
Fixes: b2101eae63ea57b571cee4a9075a4287d24ba4a4
    ("pcie: Set the "link active" in the link status register")
Cc: qemu-stable@nongnu.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/hw/compat.h  |  4 ++++
 include/hw/pci/pci.h |  3 +++
 hw/pci/pci.c         |  2 ++
 hw/pci/pcie.c        | 24 ++++++++++++++++++------
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/include/hw/compat.h b/include/hw/compat.h
index 9914e7a..e5113dc 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -80,6 +80,10 @@
         .driver   = "virtio-rng-pci",\
         .property = "any_layout",\
         .value    = "off",\
+    },{\
+        .driver   = TYPE_PCI_DEVICE,\
+        .property = "x-pcie-lnksta-dllla",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_2 \
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 74d797d..929ec2f 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -174,6 +174,9 @@ enum {
     /* PCI Express capability - Power Controller Present */
 #define QEMU_PCIE_SLTCAP_PCP_BITNR 7
     QEMU_PCIE_SLTCAP_PCP = (1 << QEMU_PCIE_SLTCAP_PCP_BITNR),
+    /* Link active status in endpoint capability is always set */
+#define QEMU_PCIE_LNKSTA_DLLLA_BITNR 8
+    QEMU_PCIE_LNKSTA_DLLLA = (1 << QEMU_PCIE_LNKSTA_DLLLA_BITNR),
 };
 
 #define TYPE_PCI_DEVICE "pci-device"
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 728c6d4..24fae16 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -62,6 +62,8 @@ static Property pci_props[] = {
                     QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
     DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
                     QEMU_PCI_CAP_SERR_BITNR, true),
+    DEFINE_PROP_BIT("x-pcie-lnksta-dllla", PCIDevice, cap_present,
+                    QEMU_PCIE_LNKSTA_DLLLA_BITNR, true),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index 9599fde..99cfb45 100644
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -45,8 +45,11 @@
  */
 
 static void
-pcie_cap_v1_fill(uint8_t *exp_cap, uint8_t port, uint8_t type, uint8_t version)
+pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
 {
+    uint8_t *exp_cap = dev->config + dev->exp.exp_cap;
+    uint8_t *cmask = dev->cmask + dev->exp.exp_cap;
+
     /* capability register
     interrupt message number defaults to 0 */
     pci_set_word(exp_cap + PCI_EXP_FLAGS,
@@ -69,7 +72,18 @@ pcie_cap_v1_fill(uint8_t *exp_cap, uint8_t port, uint8_t type, uint8_t version)
                  PCI_EXP_LNK_LS_25);
 
     pci_set_word(exp_cap + PCI_EXP_LNKSTA,
-                 PCI_EXP_LNK_MLW_1 | PCI_EXP_LNK_LS_25 |PCI_EXP_LNKSTA_DLLLA);
+                 PCI_EXP_LNK_MLW_1 | PCI_EXP_LNK_LS_25);
+
+    if (dev->cap_present & QEMU_PCIE_LNKSTA_DLLLA) {
+        pci_word_test_and_set_mask(exp_cap + PCI_EXP_LNKSTA,
+                                   PCI_EXP_LNKSTA_DLLLA);
+    }
+
+    /* We changed link status bits over time, and changing them across
+     * migrations is generally fine as hardware changes them too.
+     * Let's not bother checking.
+     */
+    pci_set_word(cmask + PCI_EXP_LNKSTA, 0);
 }
 
 int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
@@ -88,7 +102,7 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
     exp_cap = dev->config + pos;
 
     /* Filling values common with v1 */
-    pcie_cap_v1_fill(exp_cap, port, type, PCI_EXP_FLAGS_VER2);
+    pcie_cap_v1_fill(dev, port, type, PCI_EXP_FLAGS_VER2);
 
     /* Filling v2 specific values */
     pci_set_long(exp_cap + PCI_EXP_DEVCAP2,
@@ -103,7 +117,6 @@ int pcie_cap_v1_init(PCIDevice *dev, uint8_t offset, uint8_t type,
 {
     /* PCIe cap v1 init */
     int pos;
-    uint8_t *exp_cap;
 
     assert(pci_is_express(dev));
 
@@ -112,9 +125,8 @@ int pcie_cap_v1_init(PCIDevice *dev, uint8_t offset, uint8_t type,
         return pos;
     }
     dev->exp.exp_cap = pos;
-    exp_cap = dev->config + pos;
 
-    pcie_cap_v1_fill(exp_cap, port, type, PCI_EXP_FLAGS_VER1);
+    pcie_cap_v1_fill(dev, port, type, PCI_EXP_FLAGS_VER1);
 
     return pos;
 }
-- 
MST