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Message-ID: <20190815160908.GA29157@e121166-lin.cambridge.arm.com>
Date: Thu, 15 Aug 2019 17:10:51 +0100
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: "sashal@...nel.org" <sashal@...nel.org>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
KY Srinivasan <kys@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
"olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number
collision
On Wed, Aug 14, 2019 at 03:52:15PM +0000, Haiyang Zhang wrote:
> Currently in Azure cloud, for passthrough devices, the host sets the device
> instance ID's bytes 8 - 15 to a value derived from the host HWID, which is
> the same on all devices in a VM. So, the device instance ID's bytes 8 and 9
> provided by the host are no longer unique. This affects all Azure hosts
> since last year, and can cause device passthrough to VMs to fail because
Bjorn already asked, can you be a bit more specific than "since last
year" here please ?
It would be useful to understand when/how this became an issue.
> the bytes 8 and 9 are used as PCI domain number. Collision of domain
> numbers will cause the second device with the same domain number fail to
> load.
>
> In the cases of collision, we will detect and find another number that is
> not in use.
>
> Suggested-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> Acked-by: Sasha Levin <sashal@...nel.org>
> ---
> drivers/pci/controller/pci-hyperv.c | 92 +++++++++++++++++++++++++++++++------
> 1 file changed, 79 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 40b6254..31b8fd5 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -2510,6 +2510,48 @@ static void put_hvpcibus(struct hv_pcibus_device *hbus)
> complete(&hbus->remove_event);
> }
>
> +#define HVPCI_DOM_MAP_SIZE (64 * 1024)
> +static DECLARE_BITMAP(hvpci_dom_map, HVPCI_DOM_MAP_SIZE);
> +
> +/*
> + * PCI domain number 0 is used by emulated devices on Gen1 VMs, so define 0
> + * as invalid for passthrough PCI devices of this driver.
> + */
> +#define HVPCI_DOM_INVALID 0
> +
> +/**
> + * hv_get_dom_num() - Get a valid PCI domain number
> + * Check if the PCI domain number is in use, and return another number if
> + * it is in use.
> + *
> + * @dom: Requested domain number
> + *
> + * return: domain number on success, HVPCI_DOM_INVALID on failure
> + */
> +static u16 hv_get_dom_num(u16 dom)
> +{
> + unsigned int i;
> +
> + if (test_and_set_bit(dom, hvpci_dom_map) == 0)
> + return dom;
> +
> + for_each_clear_bit(i, hvpci_dom_map, HVPCI_DOM_MAP_SIZE) {
> + if (test_and_set_bit(i, hvpci_dom_map) == 0)
> + return i;
> + }
Don't you need locking around code reading/updating hvpci_dom_map ?
Thanks,
Lorenzo
> +
> + return HVPCI_DOM_INVALID;
> +}
> +
> +/**
> + * hv_put_dom_num() - Mark the PCI domain number as free
> + * @dom: Domain number to be freed
> + */
> +static void hv_put_dom_num(u16 dom)
> +{
> + clear_bit(dom, hvpci_dom_map);
> +}
> +
> /**
> * hv_pci_probe() - New VMBus channel probe, for a root PCI bus
> * @hdev: VMBus's tracking struct for this root PCI bus
> @@ -2521,6 +2563,7 @@ static int hv_pci_probe(struct hv_device *hdev,
> const struct hv_vmbus_device_id *dev_id)
> {
> struct hv_pcibus_device *hbus;
> + u16 dom_req, dom;
> int ret;
>
> /*
> @@ -2535,19 +2578,34 @@ static int hv_pci_probe(struct hv_device *hdev,
> hbus->state = hv_pcibus_init;
>
> /*
> - * The PCI bus "domain" is what is called "segment" in ACPI and
> - * other specs. Pull it from the instance ID, to get something
> - * unique. Bytes 8 and 9 are what is used in Windows guests, so
> - * do the same thing for consistency. Note that, since this code
> - * only runs in a Hyper-V VM, Hyper-V can (and does) guarantee
> - * that (1) the only domain in use for something that looks like
> - * a physical PCI bus (which is actually emulated by the
> - * hypervisor) is domain 0 and (2) there will be no overlap
> - * between domains derived from these instance IDs in the same
> - * VM.
> + * The PCI bus "domain" is what is called "segment" in ACPI and other
> + * specs. Pull it from the instance ID, to get something usually
> + * unique. In rare cases of collision, we will find out another number
> + * not in use.
> + *
> + * Note that, since this code only runs in a Hyper-V VM, Hyper-V
> + * together with this guest driver can guarantee that (1) The only
> + * domain used by Gen1 VMs for something that looks like a physical
> + * PCI bus (which is actually emulated by the hypervisor) is domain 0.
> + * (2) There will be no overlap between domains (after fixing possible
> + * collisions) in the same VM.
> */
> - hbus->sysdata.domain = hdev->dev_instance.b[9] |
> - hdev->dev_instance.b[8] << 8;
> + dom_req = hdev->dev_instance.b[8] << 8 | hdev->dev_instance.b[9];
> + dom = hv_get_dom_num(dom_req);
> +
> + if (dom == HVPCI_DOM_INVALID) {
> + dev_err(&hdev->device,
> + "Unable to use dom# 0x%hx or other numbers", dom_req);
> + ret = -EINVAL;
> + goto free_bus;
> + }
> +
> + if (dom != dom_req)
> + dev_info(&hdev->device,
> + "PCI dom# 0x%hx has collision, using 0x%hx",
> + dom_req, dom);
> +
> + hbus->sysdata.domain = dom;
>
> hbus->hdev = hdev;
> refcount_set(&hbus->remove_lock, 1);
> @@ -2562,7 +2620,7 @@ static int hv_pci_probe(struct hv_device *hdev,
> hbus->sysdata.domain);
> if (!hbus->wq) {
> ret = -ENOMEM;
> - goto free_bus;
> + goto free_dom;
> }
>
> ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0,
> @@ -2639,6 +2697,8 @@ static int hv_pci_probe(struct hv_device *hdev,
> vmbus_close(hdev->channel);
> destroy_wq:
> destroy_workqueue(hbus->wq);
> +free_dom:
> + hv_put_dom_num(hbus->sysdata.domain);
> free_bus:
> free_page((unsigned long)hbus);
> return ret;
> @@ -2720,6 +2780,9 @@ static int hv_pci_remove(struct hv_device *hdev)
> put_hvpcibus(hbus);
> wait_for_completion(&hbus->remove_event);
> destroy_workqueue(hbus->wq);
> +
> + hv_put_dom_num(hbus->sysdata.domain);
> +
> free_page((unsigned long)hbus);
> return 0;
> }
> @@ -2747,6 +2810,9 @@ static void __exit exit_hv_pci_drv(void)
>
> static int __init init_hv_pci_drv(void)
> {
> + /* Set the invalid domain number's bit, so it will not be used */
> + set_bit(HVPCI_DOM_INVALID, hvpci_dom_map);
> +
> return vmbus_driver_register(&hv_pci_drv);
> }
>
> --
> 1.8.3.1
>
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