Subject: Re: [PATCH RFC v4 12/21] PCI: Don't allow hotplugged devices to steal resources

From: Bjorn Helgaas <[email-masked]>
Date: Tue, 26 Mar 2019 15:55:33 -0500

On Mon, Mar 11, 2019 at 04:31:13PM +0300, Sergey Miroshnichenko wrote:
> When movable BARs are enabled, the PCI subsystem at first releases
> all the bridge windows and then performs an attempt to assign new
> requested resources and re-assign the existing ones.

s/performs an attempt/attempts/

I guess "new requested resources" means "resources to newly hotplugged
devices"?

> If a hotplugged device gets its resources first, there could be no
> space left to re-assign resources of already working devices, which
> is unacceptable. If this happens, this patch marks one of the new
> devices with the new introduced flag PCI_DEV_IGNORE and retries the
> resource assignment.
> 
> This patch adds a new res_mask bitmask to the struct pci_dev for
> storing the indices of assigned resources.
> 
> Signed-off-by: Sergey Miroshnichenko <[email-masked]>
> ---
>  drivers/pci/bus.c       |   5 ++
>  drivers/pci/pci.h       |  11 +++++
>  drivers/pci/probe.c     | 100 +++++++++++++++++++++++++++++++++++++++-
>  drivers/pci/setup-bus.c |  15 ++++++
>  include/linux/pci.h     |   1 +
>  5 files changed, 130 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 5cb40b2518f9..a9784144d6f2 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -311,6 +311,11 @@ void pci_bus_add_device(struct pci_dev *dev)
>  {
>  	int retval;
>  
> +	if (pci_dev_is_ignored(dev)) {
> +		pci_warn(dev, "%s: don't enable the ignored device\n", __func__);
> +		return;

I'm not sure about this.  Even if we're unable to assign space for all
the device's BARs, it still should respond to config accesses, and I
think it should show up in sysfs and lspci.

> +	}
> +
>  	/*
>  	 * Can not put in pci_device_add yet because resources
>  	 * are not assigned yet for some devices.
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index e06e8692a7b1..56b905068ac5 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -366,6 +366,7 @@ static inline bool pci_dev_is_disconnected(const struct pci_dev *dev)
>  
>  /* pci_dev priv_flags */
>  #define PCI_DEV_ADDED 0
> +#define PCI_DEV_IGNORE 1
>  
>  static inline void pci_dev_assign_added(struct pci_dev *dev, bool added)
>  {
> @@ -377,6 +378,16 @@ static inline bool pci_dev_is_added(const struct pci_dev *dev)
>  	return test_bit(PCI_DEV_ADDED, &dev->priv_flags);
>  }
>  
> +static inline void pci_dev_ignore(struct pci_dev *dev, bool ignore)
> +{
> +	assign_bit(PCI_DEV_IGNORE, &dev->priv_flags, ignore);
> +}
> +
> +static inline bool pci_dev_is_ignored(const struct pci_dev *dev)
> +{
> +	return test_bit(PCI_DEV_IGNORE, &dev->priv_flags);
> +}
> +
>  #ifdef CONFIG_PCIEAER
>  #include <linux/aer.h>
>  
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 692752c71f71..62f4058a001f 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -3248,6 +3248,23 @@ unsigned int pci_rescan_bus_bridge_resize(struct pci_dev *bridge)
>  	return max;
>  }
>  
> +static unsigned int pci_dev_res_mask(struct pci_dev *dev)
> +{
> +	unsigned int res_mask = 0;
> +	int i;
> +
> +	for (i = 0; i < PCI_BRIDGE_RESOURCES; i++) {
> +		struct resource *r = &dev->resource[i];
> +
> +		if (!r->flags || (r->flags & IORESOURCE_UNSET) || !r->parent)
> +			continue;
> +
> +		res_mask |= (1 << i);
> +	}
> +
> +	return res_mask;
> +}
> +
>  static void pci_bus_rescan_prepare(struct pci_bus *bus)
>  {
>  	struct pci_dev *dev;
> @@ -3257,6 +3274,8 @@ static void pci_bus_rescan_prepare(struct pci_bus *bus)
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		struct pci_bus *child = dev->subordinate;
>  
> +		dev->res_mask = pci_dev_res_mask(dev);
> +
>  		if (child) {
>  			pci_bus_rescan_prepare(child);
>  		} else if (dev->driver &&
> @@ -3318,6 +3337,84 @@ static void pci_setup_bridges(struct pci_bus *bus)
>  		pci_setup_bridge(bus);
>  }
>  
> +static struct pci_dev *pci_find_next_new_device(struct pci_bus *bus)
> +{
> +	struct pci_dev *dev;
> +
> +	if (!bus)
> +		return NULL;
> +
> +	list_for_each_entry(dev, &bus->devices, bus_list) {
> +		struct pci_bus *child_bus = dev->subordinate;
> +
> +		if (!pci_dev_is_added(dev) && !pci_dev_is_ignored(dev))
> +			return dev;
> +
> +		if (child_bus) {
> +			struct pci_dev *next_new_dev;
> +
> +			next_new_dev = pci_find_next_new_device(child_bus);
> +			if (next_new_dev)
> +				return next_new_dev;
> +		}
> +	}
> +
> +	return NULL;
> +}
> +
> +static bool pci_bus_validate_resources(struct pci_bus *bus)

The name of this function should tell us what the return value means.
Just from the name "pci_bus_validate_resources", I can't tell whether we
call it for side-effects, or whether true or false indicates success.

> +{
> +	struct pci_dev *dev;
> +	bool ret = true;
> +
> +	if (!bus)
> +		return false;
> +
> +	list_for_each_entry(dev, &bus->devices, bus_list) {
> +		struct pci_bus *child = dev->subordinate;
> +		unsigned int res_mask = pci_dev_res_mask(dev);
> +
> +		if (pci_dev_is_ignored(dev))
> +			continue;
> +
> +		if (dev->res_mask & ~res_mask) {
> +			pci_err(dev, "%s: Non-re-enabled resources found: 0x%x -> 0x%x\n",
> +				__func__, dev->res_mask, res_mask);

I don't think __func__ really tells users anything useful, so I would
just omit them.  Searching for the text of the message is almost as
good.

> +			ret = false;
> +		}
> +
> +		if (child && !pci_bus_validate_resources(child))
> +			ret = false;
> +	}
> +
> +	return ret;
> +}
> +
> +static void pci_reassign_root_bus_resources(struct pci_bus *root)
> +{
> +	do {
> +		struct pci_dev *next_new_dev;
> +
> +		pci_bus_release_root_bridge_resources(root);
> +		pci_assign_unassigned_root_bus_resources(root);
> +
> +		if (pci_bus_validate_resources(root))
> +			break;
> +
> +		next_new_dev = pci_find_next_new_device(root);
> +		if (!next_new_dev) {
> +			dev_err(&root->dev, "%s: failed to re-assign resources even after ignoring all the hotplugged devices\n",
> +				__func__);
> +			break;
> +		}
> +
> +		dev_warn(&root->dev, "%s: failed to re-assign resources, disable the next hotplugged device %s and retry\n",
> +			 __func__, dev_name(&next_new_dev->dev));
> +
> +		pci_dev_ignore(next_new_dev, true);
> +	} while (true);
> +}
> +
>  /**
>   * pci_rescan_bus - Scan a PCI bus for devices
>   * @bus: PCI bus to scan
> @@ -3341,8 +3438,7 @@ unsigned int pci_rescan_bus(struct pci_bus *bus)
>  
>  		max = pci_scan_child_bus(root);
>  
> -		pci_bus_release_root_bridge_resources(root);
> -		pci_assign_unassigned_root_bus_resources(root);
> +		pci_reassign_root_bus_resources(root);
>  
>  		pci_setup_bridges(root);
>  		pci_bus_rescan_done(root);
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 36a1907d9509..551108f48df7 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -131,6 +131,9 @@ static void pdev_sort_resources(struct pci_dev *dev, struct list_head *head)
>  {
>  	int i;
>  
> +	if (pci_dev_is_ignored(dev))
> +		return;
> +
>  	for (i = 0; i < PCI_NUM_RESOURCES; i++) {
>  		struct resource *r;
>  		struct pci_dev_resource *dev_res, *tmp;
> @@ -181,6 +184,9 @@ static void __dev_sort_resources(struct pci_dev *dev,
>  {
>  	u16 class = dev->class >> 8;
>  
> +	if (pci_dev_is_ignored(dev))
> +		return;
> +
>  	/* Don't touch classless devices or host bridges or ioapics.  */
>  	if (class == PCI_CLASS_NOT_DEFINED || class == PCI_CLASS_BRIDGE_HOST)
>  		return;
> @@ -284,6 +290,9 @@ static void assign_requested_resources_sorted(struct list_head *head,
>  	int idx;
>  
>  	list_for_each_entry(dev_res, head, list) {
> +		if (pci_dev_is_ignored(dev_res->dev))
> +			continue;
> +
>  		res = dev_res->res;
>  		idx = res - &dev_res->dev->resource[0];
>  		if (resource_size(res) &&
> @@ -991,6 +1000,9 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		int i;
>  
> +		if (pci_dev_is_ignored(dev))
> +			continue;
> +
>  		for (i = 0; i < PCI_NUM_RESOURCES; i++) {
>  			struct resource *r = &dev->resource[i];
>  			resource_size_t r_size;
> @@ -1353,6 +1365,9 @@ void __pci_bus_assign_resources(const struct pci_bus *bus,
>  	pbus_assign_resources_sorted(bus, realloc_head, fail_head);
>  
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
> +		if (pci_dev_is_ignored(dev))
> +			continue;
> +
>  		pdev_assign_fixed_resources(dev);
>  
>  		b = dev->subordinate;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 3d52f5538282..26aa59cb6220 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -369,6 +369,7 @@ struct pci_dev {
>  	 */
>  	unsigned int	irq;
>  	struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */
> +	unsigned int	res_mask;		/* Bitmask of assigned resources */
>  
>  	bool		match_driver;		/* Skip attaching driver */
>  
> -- 
> 2.20.1
>