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Subject[PATCH] PCI/P2PDMA: finish RCU conversion of pdev->p2pdma
Date
From: Eric Dumazet <edumazet@google.com>

While looking at pci_alloc_p2pmem() I found rcu protection
was not properly applied there, as pdev->p2pdma was
potentially read multiple times.

I decided to fix pci_alloc_p2pmem(), add __rcu qualifier
to p2pdma field of struct pci_dev, and fix all
other accesses to this field with proper rcu verbs.

Fixes: 1570175abd16 ("PCI/P2PDMA: track pgmap references per resource, not globally")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: linux-pci@vger.kernel.org
---
drivers/pci/p2pdma.c | 101 ++++++++++++++++++++++++++++++-------------
include/linux/pci.h | 2 +-
2 files changed, 73 insertions(+), 30 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 1963826303631465da2956b0e3abcec3e0fcfbc4..89095aa5c674f5b8237d543c7af2bbdc2c176e5a 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -48,10 +48,14 @@ static ssize_t size_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct pci_dev *pdev = to_pci_dev(dev);
+ struct pci_p2pdma *p2pdma;
size_t size = 0;

- if (pdev->p2pdma->pool)
- size = gen_pool_size(pdev->p2pdma->pool);
+ rcu_read_lock();
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ if (p2pdma && p2pdma->pool)
+ size = gen_pool_size(p2pdma->pool);
+ rcu_read_unlock();

return scnprintf(buf, PAGE_SIZE, "%zd\n", size);
}
@@ -61,10 +65,14 @@ static ssize_t available_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct pci_dev *pdev = to_pci_dev(dev);
+ struct pci_p2pdma *p2pdma;
size_t avail = 0;

- if (pdev->p2pdma->pool)
- avail = gen_pool_avail(pdev->p2pdma->pool);
+ rcu_read_lock();
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ if (p2pdma && p2pdma->pool)
+ avail = gen_pool_avail(p2pdma->pool);
+ rcu_read_unlock();

return scnprintf(buf, PAGE_SIZE, "%zd\n", avail);
}
@@ -74,9 +82,16 @@ static ssize_t published_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct pci_dev *pdev = to_pci_dev(dev);
+ struct pci_p2pdma *p2pdma;
+ bool published = false;
+
+ rcu_read_lock();
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ if (p2pdma)
+ published = p2pdma->p2pmem_published;
+ rcu_read_unlock();

- return scnprintf(buf, PAGE_SIZE, "%d\n",
- pdev->p2pdma->p2pmem_published);
+ return scnprintf(buf, PAGE_SIZE, "%d\n", published);
}
static DEVICE_ATTR_RO(published);

@@ -95,8 +110,9 @@ static const struct attribute_group p2pmem_group = {
static void pci_p2pdma_release(void *data)
{
struct pci_dev *pdev = data;
- struct pci_p2pdma *p2pdma = pdev->p2pdma;
+ struct pci_p2pdma *p2pdma;

+ p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
if (!p2pdma)
return;

@@ -128,16 +144,14 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
if (error)
goto out_pool_destroy;

- pdev->p2pdma = p2p;
-
error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
if (error)
goto out_pool_destroy;

+ rcu_assign_pointer(pdev->p2pdma, p2p);
return 0;

out_pool_destroy:
- pdev->p2pdma = NULL;
gen_pool_destroy(p2p->pool);
out:
devm_kfree(&pdev->dev, p2p);
@@ -159,6 +173,7 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
{
struct pci_p2pdma_pagemap *p2p_pgmap;
struct dev_pagemap *pgmap;
+ struct pci_p2pdma *p2pdma;
void *addr;
int error;

@@ -200,7 +215,8 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
goto pgmap_free;
}

- error = gen_pool_add_owner(pdev->p2pdma->pool, (unsigned long)addr,
+ p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+ error = gen_pool_add_owner(p2pdma->pool, (unsigned long)addr,
pci_bus_address(pdev, bar) + offset,
range_len(&pgmap->range), dev_to_node(&pdev->dev),
pgmap->ref);
@@ -476,6 +492,7 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
int *dist, bool *acs_redirects, struct seq_buf *acs_list)
{
enum pci_p2pdma_map_type map_type;
+ struct pci_p2pdma *p2pdma;

map_type = __upstream_bridge_distance(provider, client, dist,
acs_redirects, acs_list);
@@ -486,10 +503,12 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
}

- if (provider->p2pdma)
- xa_store(&provider->p2pdma->map_types, map_types_idx(client),
- xa_mk_value(map_type), GFP_KERNEL);
-
+ rcu_read_lock();
+ p2pdma = rcu_dereference(provider->p2pdma);
+ if (p2pdma)
+ xa_store(&p2pdma->map_types, map_types_idx(client),
+ xa_mk_value(map_type), GFP_ATOMIC);
+ rcu_read_unlock();
return map_type;
}

@@ -595,7 +614,15 @@ EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);
*/
bool pci_has_p2pmem(struct pci_dev *pdev)
{
- return pdev->p2pdma && pdev->p2pdma->p2pmem_published;
+ struct pci_p2pdma *p2pdma;
+ bool res;
+
+ rcu_read_lock();
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ res = p2pdma && p2pdma->p2pmem_published;
+ rcu_read_unlock();
+
+ return res;
}
EXPORT_SYMBOL_GPL(pci_has_p2pmem);

@@ -675,6 +702,7 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
{
void *ret = NULL;
struct percpu_ref *ref;
+ struct pci_p2pdma *p2pdma;

/*
* Pairs with synchronize_rcu() in pci_p2pdma_release() to
@@ -682,16 +710,17 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
* read-lock.
*/
rcu_read_lock();
- if (unlikely(!pdev->p2pdma))
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ if (unlikely(!p2pdma))
goto out;

- ret = (void *)gen_pool_alloc_owner(pdev->p2pdma->pool, size,
+ ret = (void *)gen_pool_alloc_owner(p2pdma->pool, size,
(void **) &ref);
if (!ret)
goto out;

if (unlikely(!percpu_ref_tryget_live(ref))) {
- gen_pool_free(pdev->p2pdma->pool, (unsigned long) ret, size);
+ gen_pool_free(p2pdma->pool, (unsigned long) ret, size);
ret = NULL;
goto out;
}
@@ -710,9 +739,9 @@ EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
{
struct percpu_ref *ref;
+ struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);

- gen_pool_free_owner(pdev->p2pdma->pool, (uintptr_t)addr, size,
- (void **) &ref);
+ gen_pool_free_owner(p2pdma->pool, (uintptr_t)addr, size, (void **) &ref);
percpu_ref_put(ref);
}
EXPORT_SYMBOL_GPL(pci_free_p2pmem);
@@ -725,9 +754,12 @@ EXPORT_SYMBOL_GPL(pci_free_p2pmem);
*/
pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
{
+ struct pci_p2pdma *p2pdma;
+
if (!addr)
return 0;
- if (!pdev->p2pdma)
+ p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+ if (!p2pdma)
return 0;

/*
@@ -735,7 +767,7 @@ pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
* bus address as the physical address. So gen_pool_virt_to_phys()
* actually returns the bus address despite the misleading name.
*/
- return gen_pool_virt_to_phys(pdev->p2pdma->pool, (unsigned long)addr);
+ return gen_pool_virt_to_phys(p2pdma->pool, (unsigned long)addr);
}
EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);

@@ -806,19 +838,30 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);
*/
void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
{
- if (pdev->p2pdma)
- pdev->p2pdma->p2pmem_published = publish;
+ struct pci_p2pdma *p2pdma;
+
+ rcu_read_lock();
+ p2pdma = rcu_dereference(pdev->p2pdma);
+ if (p2pdma)
+ p2pdma->p2pmem_published = publish;
+ rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(pci_p2pmem_publish);

static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider,
struct pci_dev *client)
{
- if (!provider->p2pdma)
- return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+ enum pci_p2pdma_map_type type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
+ struct pci_p2pdma *p2pdma;

- return xa_to_value(xa_load(&provider->p2pdma->map_types,
- map_types_idx(client)));
+ rcu_read_lock();
+ p2pdma = rcu_dereference(provider->p2pdma);
+
+ if (p2pdma)
+ type = xa_to_value(xa_load(&p2pdma->map_types,
+ map_types_idx(client)));
+ rcu_read_unlock();
+ return type;
}

static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 24306504226ab665be7323549d0759da1b7ac715..6abdebe2aeb1676da08f03e05e5ecb26f0b08cd6 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -497,7 +497,7 @@ struct pci_dev {
u16 pasid_features;
#endif
#ifdef CONFIG_PCI_P2PDMA
- struct pci_p2pdma *p2pdma;
+ struct pci_p2pdma __rcu *p2pdma;
#endif
u16 acs_cap; /* ACS Capability offset */
phys_addr_t rom; /* Physical address if not from BAR */
--
2.32.0.93.g670b81a890-goog
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