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Message-ID: <20200727111852.GA14239@e121166-lin.cambridge.arm.com>
Date: Mon, 27 Jul 2020 12:18:52 +0100
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Wei Hu <weh@...rosoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
wei.liu@...nel.org, robh@...nel.org, bhelgaas@...gle.com,
linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, decui@...rosoft.com,
mikelley@...rosoft.com
Subject: Re: [PATCH v4] PCI: hv: Fix a timing issue which causes kdump to
fail occasionally
On Mon, Jul 27, 2020 at 03:17:31PM +0800, Wei Hu wrote:
> Kdump could fail sometime on Hyper-V guest over Accelerated Network
> interface. This is because the retry in hv_pci_enter_d0() releases
> child device strurctures in hv_pci_bus_exit(). Although there is
> a second asynchronous device relations message sending from the host,
> if this message arrives guest after hv_send_resource_allocated() is
> called, the retry would fail.
>
> Fix the problem by moving retry to hv_pci_probe() and starting retry
> from hv_pci_query_relations() call. This will cause a device relations
> message to arrive guest synchronously. The guest would be able to
> rebuild the child device structures before calling
> hv_send_resource_allocated().
>
> This problem only happens on Accelerated Network or SRIOV devices as
> only such devices currently are attached under vmbus PCI bridge.
>
> Fixes: c81992e7f4aa ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
> Signed-off-by: Wei Hu <weh@...rosoft.com>
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> ---
> v2: Adding Fixes tag according to Michael Kelley's review comment.
> v3: Fix couple typos and reword commit message to make it clearer.
> Thanks the comments from Bjorn Helgaas.
> v4: Adding more problem descritpions in the commit message
> and code upon request from Lorenze Pieralisi.
>
> drivers/pci/controller/pci-hyperv.c | 71 +++++++++++++++--------------
> 1 file changed, 37 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
I edited commit log and a comment in the code to fix a typo and pushed
out to pci/hv.
Thanks,
Lorenzo
> index bf40ff09c99d..d1758986fbc9 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -2759,10 +2759,8 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
> struct pci_bus_d0_entry *d0_entry;
> struct hv_pci_compl comp_pkt;
> struct pci_packet *pkt;
> - bool retry = true;
> int ret;
>
> -enter_d0_retry:
> /*
> * Tell the host that the bus is ready to use, and moved into the
> * powered-on state. This includes telling the host which region
> @@ -2789,38 +2787,6 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
> if (ret)
> goto exit;
>
> - /*
> - * In certain case (Kdump) the pci device of interest was
> - * not cleanly shut down and resource is still held on host
> - * side, the host could return invalid device status.
> - * We need to explicitly request host to release the resource
> - * and try to enter D0 again.
> - */
> - if (comp_pkt.completion_status < 0 && retry) {
> - retry = false;
> -
> - dev_err(&hdev->device, "Retrying D0 Entry\n");
> -
> - /*
> - * Hv_pci_bus_exit() calls hv_send_resource_released()
> - * to free up resources of its child devices.
> - * In the kdump kernel we need to set the
> - * wslot_res_allocated to 255 so it scans all child
> - * devices to release resources allocated in the
> - * normal kernel before panic happened.
> - */
> - hbus->wslot_res_allocated = 255;
> -
> - ret = hv_pci_bus_exit(hdev, true);
> -
> - if (ret == 0) {
> - kfree(pkt);
> - goto enter_d0_retry;
> - }
> - dev_err(&hdev->device,
> - "Retrying D0 failed with ret %d\n", ret);
> - }
> -
> if (comp_pkt.completion_status < 0) {
> dev_err(&hdev->device,
> "PCI Pass-through VSP failed D0 Entry with status %x\n",
> @@ -3058,6 +3024,7 @@ static int hv_pci_probe(struct hv_device *hdev,
> struct hv_pcibus_device *hbus;
> u16 dom_req, dom;
> char *name;
> + bool enter_d0_retry = true;
> int ret;
>
> /*
> @@ -3178,11 +3145,47 @@ static int hv_pci_probe(struct hv_device *hdev,
> if (ret)
> goto free_fwnode;
>
> +retry:
> ret = hv_pci_query_relations(hdev);
> if (ret)
> goto free_irq_domain;
>
> ret = hv_pci_enter_d0(hdev);
> + /*
> + * In certain case (Kdump) the pci device of interest was
> + * not cleanly shut down and resource is still held on host
> + * side, the host could return invalid device status.
> + * We need to explicitly request host to release the resource
> + * and try to enter D0 again.
> + * Since the hv_pci_bus_exit() call releases structures
> + * of all its child devices, we need to start the retry from
> + * hv_pci_query_relations() call, requesting host to send
> + * the synchronous child device relations message before this
> + * information is needed in hv_send_resources_allocated()
> + * call later .
> + */
> + if (ret == -EPROTO && enter_d0_retry) {
> + enter_d0_retry = false;
> +
> + dev_err(&hdev->device, "Retrying D0 Entry\n");
> +
> + /*
> + * Hv_pci_bus_exit() calls hv_send_resources_released()
> + * to free up resources of its child devices.
> + * In the kdump kernel we need to set the
> + * wslot_res_allocated to 255 so it scans all child
> + * devices to release resources allocated in the
> + * normal kernel before panic happened.
> + */
> + hbus->wslot_res_allocated = 255;
> + ret = hv_pci_bus_exit(hdev, true);
> +
> + if (ret == 0)
> + goto retry;
> +
> + dev_err(&hdev->device,
> + "Retrying D0 failed with ret %d\n", ret);
> + }
> if (ret)
> goto free_irq_domain;
>
> --
> 2.20.1
>
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