[PATCH v5,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number collision

[PATCH v5,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number collision

[Haiyang Zhang]

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
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@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Acked-by: Sasha Levin <sashal@kernel.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;
+	}
+
+	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

[PATCH v5,2/2] PCI: hv: Use bytes 4 and 5 from instance ID as the PCI domain numbers

[Haiyang Zhang]

As recommended by Azure host team, the bytes 4, 5 have more uniqueness
(info entropy) than bytes 8, 9. So now we use bytes 4, 5 as the PCI domain
numbers. On older hosts, bytes 4, 5 can also be used -- no backward
compatibility issues here. The chance of collision is greatly reduced.

In the rare cases of collision, the driver code detects and finds another
number that is not in use.

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Acked-by: Sasha Levin <sashal@kernel.org>
---
 drivers/pci/controller/pci-hyperv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 31b8fd5..4f3d97e 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -2590,7 +2590,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 	 * (2) There will be no overlap between domains (after fixing possible
 	 * collisions) in the same VM.
 	 */
-	dom_req = hdev->dev_instance.b[8] << 8 | hdev->dev_instance.b[9];
+	dom_req = hdev->dev_instance.b[5] << 8 | hdev->dev_instance.b[4];
 	dom = hv_get_dom_num(dom_req);
 
 	if (dom == HVPCI_DOM_INVALID) {
-- 
1.8.3.1

Re: [PATCH v5,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number collision

[Lorenzo Pieralisi]

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@microsoft.com>
> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> Acked-by: Sasha Levin <sashal@kernel.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
> 

RE: [PATCH v5,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number collision

[Haiyang Zhang]

> -----Original Message-----
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Sent: Thursday, August 15, 2019 12:11 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: sashal@kernel.org; bhelgaas@google.com; linux-
> hyperv@vger.kernel.org; linux-pci@vger.kernel.org; KY Srinivasan
> <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> olaf@aepfle.de; vkuznets <vkuznets@redhat.com>; linux-
> kernel@vger.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 host change happens around July 2018. The Azure roll out takes
multi weeks, so there is no specific date. I will include the Month
Year in the log.

> 
> > 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@microsoft.com>
> > Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> > Acked-by: Sasha Levin <sashal@kernel.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 ?

If the bit changes after for_each_clear_bit() considers it as a "clear bit" - the
test_and_set_bit() does test&set in an atomic operation - the return value
will be 1 instead of 0. Then the loop will continue to the next clear bit, until
the test_and_set_bit() is successful. So no locking is necessary here.

Thanks,
- Haiyang