[Qemu-devel] [PATCH v2] pcie: fix device hotplug failure at the meantime of VM boot

[Qemu-devel] [PATCH v2] pcie: fix device hotplug failure at the meantime of VM boot

[Zhangbo (Oscar)]

If the PCI_EXP_LNKSTA_DLLLA capability is set by default, linux kernel will send 
PDC event to detect whether there is a device in pcie slot. If a device is pluged
in the pcie-root-port at the same time, hot-plug device will send ABP + PDC
events to the kernel. The VM kernel will wrongly unplug the device if two PDC
events get too close. Thus we'd better set the PCI_EXP_LNKSTA_DLLLA
capability only in hotplug callback.

By the way, we should clean up the PCI_EXP_LNKSTA_DLLLA capability during
unplug to avoid VM restart or migration failure which will enter the same
abnormal scenario as above.

Signed-off-by: Li Mingwang <limingwang@huawei.com>
Signed-off-by: Fang Ying <fangying1@huawei.com>
Signed-off-by: Zhang Bo <oscar.zhangbo@huawei.com>
---
 hw/pci/pcie.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index a6beb56..174f392 100644
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -75,10 +75,6 @@ pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
                  QEMU_PCI_EXP_LNKSTA_NLW(QEMU_PCI_EXP_LNK_X1) |
                  QEMU_PCI_EXP_LNKSTA_CLS(QEMU_PCI_EXP_LNK_2_5GT));
 
-    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.
@@ -484,6 +480,11 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev,
         return;
     }
 
+    if (pci_dev->cap_present & QEMU_PCIE_LNKSTA_DLLLA) {
+        pci_word_test_and_clear_mask(exp_cap + PCI_EXP_LNKSTA,
+                                     PCI_EXP_LNKSTA_DLLLA);
+    }
+
     pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
 }
 
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH v2] pcie: fix device hotplug failure at the meantime of VM boot

[Michael S. Tsirkin]

On Tue, Jul 23, 2019 at 09:31:30AM +0000, Zhangbo (Oscar) wrote:
> If the PCI_EXP_LNKSTA_DLLLA capability is set by default, linux kernel will send 
> PDC event to detect whether there is a device in pcie slot. If a device is pluged
> in the pcie-root-port at the same time, hot-plug device will send ABP + PDC
> events to the kernel. The VM kernel will wrongly unplug the device if two PDC
> events get too close. Thus we'd better set the PCI_EXP_LNKSTA_DLLLA
> capability only in hotplug callback.
> 
> By the way, we should clean up the PCI_EXP_LNKSTA_DLLLA capability during
> unplug to avoid VM restart or migration failure which will enter the same
> abnormal scenario as above.
> 
> Signed-off-by: Li Mingwang <limingwang@huawei.com>
> Signed-off-by: Fang Ying <fangying1@huawei.com>
> Signed-off-by: Zhang Bo <oscar.zhangbo@huawei.com>


I responded on v1 before seeing v2. As there's no change to patch
or commit log, same comments apply.



> ---
>  hw/pci/pcie.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index a6beb56..174f392 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -75,10 +75,6 @@ pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
>                   QEMU_PCI_EXP_LNKSTA_NLW(QEMU_PCI_EXP_LNK_X1) |
>                   QEMU_PCI_EXP_LNKSTA_CLS(QEMU_PCI_EXP_LNK_2_5GT));
>  
> -    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.
> @@ -484,6 +480,11 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev,
>          return;
>      }
>  
> +    if (pci_dev->cap_present & QEMU_PCIE_LNKSTA_DLLLA) {
> +        pci_word_test_and_clear_mask(exp_cap + PCI_EXP_LNKSTA,
> +                                     PCI_EXP_LNKSTA_DLLLA);
> +    }
> +
>      pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
>  }
>  
> -- 
> 1.8.3.1