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authorMatthew Wilcox <matthew@wil.cx>2006-10-19 09:41:28 -0600
committerGreg Kroah-Hartman <gregkh@suse.de>2006-12-01 14:36:58 -0800
commit7ea7e98fd8d02351c43ef4ab35d70f3aaa26c31d (patch)
treecb37b18402c2b82cc227ad6bd1ab3d57cf677ff3 /drivers/pci/access.c
parent50bf14b3ff05fb6e10688021b96f95d30a300f8d (diff)
PCI: Block on access to temporarily unavailable pci device
The existing implementation of pci_block_user_cfg_access() was recently criticised for providing out of date information and for returning errors on write, which applications won't be expecting. This reimplementation uses a global wait queue and a bit per device. I've open-coded prepare_to_wait() / finish_wait() as I could optimise it significantly by knowing that the pci_lock protected us at all points. It looked a bit funny to be doing a spin_unlock_irqsave(); schedule(), so I used spin_lock_irq() for the _user versions of pci_read_config and pci_write_config. Not carrying a flags pointer around made the code much less nasty. Attempts to block an already blocked device hit a BUG() and attempts to unblock an already unblocked device hit a WARN(). If we need to block access to a device from userspace, it's because it's unsafe for even another bit of the kernel to access the device. An attempt to block a device for a second time means we're about to access the device to perform some other operation, which could provoke undefined behaviour from the device. Signed-off-by: Matthew Wilcox <matthew@wil.cx> Acked-by: Adam Belay <abelay@novell.com> Acked-by: Alan Cox <alan@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/pci/access.c')
-rw-r--r--drivers/pci/access.c75
1 files changed, 47 insertions, 28 deletions
diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index ea16805a153..73a58c73d52 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -1,6 +1,7 @@
#include <linux/pci.h>
#include <linux/module.h>
#include <linux/ioport.h>
+#include <linux/wait.h>
#include "pci.h"
@@ -63,30 +64,42 @@ EXPORT_SYMBOL(pci_bus_write_config_byte);
EXPORT_SYMBOL(pci_bus_write_config_word);
EXPORT_SYMBOL(pci_bus_write_config_dword);
-static u32 pci_user_cached_config(struct pci_dev *dev, int pos)
-{
- u32 data;
+/*
+ * The following routines are to prevent the user from accessing PCI config
+ * space when it's unsafe to do so. Some devices require this during BIST and
+ * we're required to prevent it during D-state transitions.
+ *
+ * We have a bit per device to indicate it's blocked and a global wait queue
+ * for callers to sleep on until devices are unblocked.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(pci_ucfg_wait);
- data = dev->saved_config_space[pos/sizeof(dev->saved_config_space[0])];
- data >>= (pos % sizeof(dev->saved_config_space[0])) * 8;
- return data;
+static noinline void pci_wait_ucfg(struct pci_dev *dev)
+{
+ DECLARE_WAITQUEUE(wait, current);
+
+ __add_wait_queue(&pci_ucfg_wait, &wait);
+ do {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ spin_unlock_irq(&pci_lock);
+ schedule();
+ spin_lock_irq(&pci_lock);
+ } while (dev->block_ucfg_access);
+ __remove_wait_queue(&pci_ucfg_wait, &wait);
}
#define PCI_USER_READ_CONFIG(size,type) \
int pci_user_read_config_##size \
(struct pci_dev *dev, int pos, type *val) \
{ \
- unsigned long flags; \
int ret = 0; \
u32 data = -1; \
if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER; \
- spin_lock_irqsave(&pci_lock, flags); \
- if (likely(!dev->block_ucfg_access)) \
- ret = dev->bus->ops->read(dev->bus, dev->devfn, \
+ spin_lock_irq(&pci_lock); \
+ if (unlikely(dev->block_ucfg_access)) pci_wait_ucfg(dev); \
+ ret = dev->bus->ops->read(dev->bus, dev->devfn, \
pos, sizeof(type), &data); \
- else if (pos < sizeof(dev->saved_config_space)) \
- data = pci_user_cached_config(dev, pos); \
- spin_unlock_irqrestore(&pci_lock, flags); \
+ spin_unlock_irq(&pci_lock); \
*val = (type)data; \
return ret; \
}
@@ -95,14 +108,13 @@ int pci_user_read_config_##size \
int pci_user_write_config_##size \
(struct pci_dev *dev, int pos, type val) \
{ \
- unsigned long flags; \
int ret = -EIO; \
if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER; \
- spin_lock_irqsave(&pci_lock, flags); \
- if (likely(!dev->block_ucfg_access)) \
- ret = dev->bus->ops->write(dev->bus, dev->devfn, \
+ spin_lock_irq(&pci_lock); \
+ if (unlikely(dev->block_ucfg_access)) pci_wait_ucfg(dev); \
+ ret = dev->bus->ops->write(dev->bus, dev->devfn, \
pos, sizeof(type), val); \
- spin_unlock_irqrestore(&pci_lock, flags); \
+ spin_unlock_irq(&pci_lock); \
return ret; \
}
@@ -117,21 +129,23 @@ PCI_USER_WRITE_CONFIG(dword, u32)
* pci_block_user_cfg_access - Block userspace PCI config reads/writes
* @dev: pci device struct
*
- * This function blocks any userspace PCI config accesses from occurring.
- * When blocked, any writes will be bit bucketed and reads will return the
- * data saved using pci_save_state for the first 64 bytes of config
- * space and return 0xff for all other config reads.
- **/
+ * When user access is blocked, any reads or writes to config space will
+ * sleep until access is unblocked again. We don't allow nesting of
+ * block/unblock calls.
+ */
void pci_block_user_cfg_access(struct pci_dev *dev)
{
unsigned long flags;
+ int was_blocked;
- pci_save_state(dev);
-
- /* spinlock to synchronize with anyone reading config space now */
spin_lock_irqsave(&pci_lock, flags);
+ was_blocked = dev->block_ucfg_access;
dev->block_ucfg_access = 1;
spin_unlock_irqrestore(&pci_lock, flags);
+
+ /* If we BUG() inside the pci_lock, we're guaranteed to hose
+ * the machine */
+ BUG_ON(was_blocked);
}
EXPORT_SYMBOL_GPL(pci_block_user_cfg_access);
@@ -140,14 +154,19 @@ EXPORT_SYMBOL_GPL(pci_block_user_cfg_access);
* @dev: pci device struct
*
* This function allows userspace PCI config accesses to resume.
- **/
+ */
void pci_unblock_user_cfg_access(struct pci_dev *dev)
{
unsigned long flags;
- /* spinlock to synchronize with anyone reading saved config space */
spin_lock_irqsave(&pci_lock, flags);
+
+ /* This indicates a problem in the caller, but we don't need
+ * to kill them, unlike a double-block above. */
+ WARN_ON(!dev->block_ucfg_access);
+
dev->block_ucfg_access = 0;
+ wake_up_all(&pci_ucfg_wait);
spin_unlock_irqrestore(&pci_lock, flags);
}
EXPORT_SYMBOL_GPL(pci_unblock_user_cfg_access);