Re: [PATCH v2 1/7] iommu/io-pgtable: Introduce dynamic io-pgtable fmt registration

From: Robin Murphy
Date: Tue Dec 22 2020 - 14:28:32 EST

On 2020-12-22 00:44, Isaac J. Manjarres wrote:
The io-pgtable code constructs an array of init functions for each
page table format at compile time. This is not ideal, as this
increases the footprint of the io-pgtable code, as well as prevents
io-pgtable formats from being built as kernel modules.

In preparation for modularizing the io-pgtable formats, switch to a
dynamic registration scheme, where each io-pgtable format can register
their init functions with the io-pgtable code at boot or module
insertion time.

Signed-off-by: Isaac J. Manjarres <isaacm@xxxxxxxxxxxxxx>
---
drivers/iommu/io-pgtable-arm-v7s.c | 34 +++++++++++++-
drivers/iommu/io-pgtable-arm.c | 90 ++++++++++++++++++++++++++----------
drivers/iommu/io-pgtable.c | 94 ++++++++++++++++++++++++++++++++------
include/linux/io-pgtable.h | 51 +++++++++++++--------
4 files changed, 209 insertions(+), 60 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
index 1d92ac9..89aad2f 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -28,6 +28,7 @@
#include <linux/iommu.h>
#include <linux/kernel.h>
#include <linux/kmemleak.h>
+#include <linux/module.h>
#include <linux/sizes.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
@@ -835,7 +836,8 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
return NULL;
}
-struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns = {
+static struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns = {
+ .fmt = ARM_V7S,
.alloc = arm_v7s_alloc_pgtable,
.free = arm_v7s_free_pgtable,
};
@@ -982,5 +984,33 @@ static int __init arm_v7s_do_selftests(void)
pr_info("self test ok\n");
return 0;
}
-subsys_initcall(arm_v7s_do_selftests);
+#else
+static int arm_v7s_do_selftests(void)
+{
+ return 0;
+}
#endif
+
+static int __init arm_v7s_init(void)
+{
+ int ret;
+
+ ret = io_pgtable_ops_register(&io_pgtable_arm_v7s_init_fns);
+ if (ret < 0) {
+ pr_err("Failed to register ARM V7S format\n");

Super-nit: I think "v7s" should probably be lowercase there. Also general consistency WRT to showing the error code and whether or not to abbreviate "format" would be nice.

+ return ret;
+ }
+
+ ret = arm_v7s_do_selftests();
+ if (ret < 0)
+ io_pgtable_ops_unregister(&io_pgtable_arm_v7s_init_fns);
+
+ return ret;
+}
+core_initcall(arm_v7s_init);
+
+static void __exit arm_v7s_exit(void)
+{
+ io_pgtable_ops_unregister(&io_pgtable_arm_v7s_init_fns);
+}
+module_exit(arm_v7s_exit);
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 87def58..ff0ea2f 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -13,6 +13,7 @@
#include <linux/bitops.h>
#include <linux/io-pgtable.h>
#include <linux/kernel.h>
+#include <linux/module.h>
#include <linux/sizes.h>
#include <linux/slab.h>
#include <linux/types.h>
@@ -1043,29 +1044,32 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
return NULL;
}
-struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s1_init_fns = {
- .alloc = arm_64_lpae_alloc_pgtable_s1,
- .free = arm_lpae_free_pgtable,
-};
-
-struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
- .alloc = arm_64_lpae_alloc_pgtable_s2,
- .free = arm_lpae_free_pgtable,
-};
-
-struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s1_init_fns = {
- .alloc = arm_32_lpae_alloc_pgtable_s1,
- .free = arm_lpae_free_pgtable,
-};
-
-struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
- .alloc = arm_32_lpae_alloc_pgtable_s2,
- .free = arm_lpae_free_pgtable,
-};
-
-struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
- .alloc = arm_mali_lpae_alloc_pgtable,
- .free = arm_lpae_free_pgtable,
+static struct io_pgtable_init_fns io_pgtable_arm_lpae_init_fns[] = {
+ {
+ .fmt = ARM_32_LPAE_S1,
+ .alloc = arm_32_lpae_alloc_pgtable_s1,
+ .free = arm_lpae_free_pgtable,
+ },
+ {
+ .fmt = ARM_32_LPAE_S2,
+ .alloc = arm_32_lpae_alloc_pgtable_s2,
+ .free = arm_lpae_free_pgtable,
+ },
+ {
+ .fmt = ARM_64_LPAE_S1,
+ .alloc = arm_64_lpae_alloc_pgtable_s1,
+ .free = arm_lpae_free_pgtable,
+ },
+ {
+ .fmt = ARM_64_LPAE_S2,
+ .alloc = arm_64_lpae_alloc_pgtable_s2,
+ .free = arm_lpae_free_pgtable,
+ },
+ {
+ .fmt = ARM_MALI_LPAE,
+ .alloc = arm_mali_lpae_alloc_pgtable,
+ .free = arm_lpae_free_pgtable,
+ },
};
#ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
@@ -1250,5 +1254,43 @@ static int __init arm_lpae_do_selftests(void)
pr_info("selftest: completed with %d PASS %d FAIL\n", pass, fail);
return fail ? -EFAULT : 0;
}
-subsys_initcall(arm_lpae_do_selftests);
+#else
+static int __init arm_lpae_do_selftests(void)
+{
+ return 0;
+}
#endif
+
+static int __init arm_lpae_init(void)
+{
+ int ret, i;
+
+ for (i = 0; i < ARRAY_SIZE(io_pgtable_arm_lpae_init_fns); i++) {
+ ret = io_pgtable_ops_register(&io_pgtable_arm_lpae_init_fns[i]);
+ if (ret < 0) {
+ pr_err("Failed to register ARM LPAE fmt: %d\n");
+ goto err_io_pgtable_register;
+ }
+ }
+
+ ret = arm_lpae_do_selftests();
+ if (ret < 0)
+ goto err_io_pgtable_register;
+
+ return 0;
+
+err_io_pgtable_register:
+ for (i = i - 1; i >= 0; i--)

Personally I find "while (i--)" a bit clearer for this kind of unwinding, but maybe post-decrement isn't to everyone's taste.

+ io_pgtable_ops_unregister(&io_pgtable_arm_lpae_init_fns[i]);
+ return ret;
+}
+core_initcall(arm_lpae_init);
+
+static void __exit arm_lpae_exit(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(io_pgtable_arm_lpae_init_fns); i++)
+ io_pgtable_ops_unregister(&io_pgtable_arm_lpae_init_fns[i]);
+}
+module_exit(arm_lpae_exit);
diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
index 94394c8..2c6eb2e 100644
--- a/drivers/iommu/io-pgtable.c
+++ b/drivers/iommu/io-pgtable.c
@@ -10,33 +10,45 @@
#include <linux/bug.h>
#include <linux/io-pgtable.h>
#include <linux/kernel.h>
+#include <linux/rwlock.h>
+#include <linux/slab.h>
#include <linux/types.h>
-static const struct io_pgtable_init_fns *
-io_pgtable_init_table[IO_PGTABLE_NUM_FMTS] = {
-#ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE
- [ARM_32_LPAE_S1] = &io_pgtable_arm_32_lpae_s1_init_fns,
- [ARM_32_LPAE_S2] = &io_pgtable_arm_32_lpae_s2_init_fns,
- [ARM_64_LPAE_S1] = &io_pgtable_arm_64_lpae_s1_init_fns,
- [ARM_64_LPAE_S2] = &io_pgtable_arm_64_lpae_s2_init_fns,
- [ARM_MALI_LPAE] = &io_pgtable_arm_mali_lpae_init_fns,
-#endif
-#ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S
- [ARM_V7S] = &io_pgtable_arm_v7s_init_fns,
-#endif
+struct io_pgtable_init_fns_node {
+ struct io_pgtable_init_fns *fns;
+ struct list_head list;
};
+static LIST_HEAD(io_pgtable_init_fns_list);
+static DEFINE_RWLOCK(io_pgtable_init_fns_list_lock);
+
+static struct io_pgtable_init_fns *io_pgtable_get_init_fns(enum io_pgtable_fmt fmt)
+{
+ struct io_pgtable_init_fns_node *iter;
+ struct io_pgtable_init_fns *fns = NULL;
+
+ read_lock(&io_pgtable_init_fns_list_lock);
+ list_for_each_entry(iter, &io_pgtable_init_fns_list, list)
+ if (iter->fns->fmt == fmt) {
+ fns = iter->fns;
+ break;
+ }
+ read_unlock(&io_pgtable_init_fns_list_lock);
+
+ return fns;
+}

I think it would be a lot easier to stick with a simple array indexed by enum - that way you can just set/clear/test entries without needing to worry about locking. Basically just remove the const and the initialisers from the existing one ;)

(and if you think you're concerned about memory, consider that just the list head plus lock is already half the size of the table)

Other than that, I think this all looks pretty promising - I'd suggest sending a non-RFC after rc1 so that it gets everyone's proper attention.

Thanks,
Robin.

+
struct io_pgtable_ops *alloc_io_pgtable_ops(enum io_pgtable_fmt fmt,
struct io_pgtable_cfg *cfg,
void *cookie)
{
struct io_pgtable *iop;
- const struct io_pgtable_init_fns *fns;
+ struct io_pgtable_init_fns *fns;
if (fmt >= IO_PGTABLE_NUM_FMTS)
return NULL;
- fns = io_pgtable_init_table[fmt];
+ fns = io_pgtable_get_init_fns(fmt);
if (!fns)
return NULL;
@@ -59,12 +71,64 @@ EXPORT_SYMBOL_GPL(alloc_io_pgtable_ops);
void free_io_pgtable_ops(struct io_pgtable_ops *ops)
{
struct io_pgtable *iop;
+ struct io_pgtable_init_fns *fns;
if (!ops)
return;
iop = io_pgtable_ops_to_pgtable(ops);
io_pgtable_tlb_flush_all(iop);
- io_pgtable_init_table[iop->fmt]->free(iop);
+ fns = io_pgtable_get_init_fns(iop->fmt);
+ if (fns)
+ fns->free(iop);
}
EXPORT_SYMBOL_GPL(free_io_pgtable_ops);
+
+int io_pgtable_ops_register(struct io_pgtable_init_fns *init_fns)
+{
+ struct io_pgtable_init_fns_node *iter, *fns_node;
+ int ret = 0;
+
+ if (!init_fns || init_fns->fmt >= IO_PGTABLE_NUM_FMTS ||
+ !init_fns->alloc || !init_fns->free)
+ return -EINVAL;
+
+ fns_node = kzalloc(sizeof(*fns_node), GFP_KERNEL);
+ if (!fns_node)
+ return -ENOMEM;
+
+ write_lock(&io_pgtable_init_fns_list_lock);
+ list_for_each_entry(iter, &io_pgtable_init_fns_list, list)
+ if (iter->fns->fmt == init_fns->fmt) {
+ ret = -EEXIST;
+ kfree(fns_node);
+ break;
+ }
+
+ if (!ret) {
+ fns_node->fns = init_fns;
+ INIT_LIST_HEAD(&fns_node->list);
+ list_add_tail(&fns_node->list, &io_pgtable_init_fns_list);
+ }
+ write_unlock(&io_pgtable_init_fns_list_lock);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(io_pgtable_ops_register);
+
+void io_pgtable_ops_unregister(struct io_pgtable_init_fns *init_fns)
+{
+ struct io_pgtable_init_fns_node *iter, *tmp;
+
+ if (!init_fns)
+ return;
+
+ write_lock(&io_pgtable_init_fns_list_lock);
+ list_for_each_entry_safe(iter, tmp, &io_pgtable_init_fns_list, list)
+ if (iter->fns == init_fns) {
+ list_del(&iter->list);
+ kfree(iter);
+ break;
+ }
+ write_unlock(&io_pgtable_init_fns_list_lock);
+}
+EXPORT_SYMBOL_GPL(io_pgtable_ops_unregister);
diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index ea727eb..45b367ce 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -163,6 +163,38 @@ struct io_pgtable_ops {
};
/**
+ * struct io_pgtable_init_fns - Alloc/free a set of page tables for a
+ * particular format.
+ *
+ * @fmt: The page table format.
+ * @alloc: Allocate a set of page tables described by cfg.
+ * @free: Free the page tables associated with iop.
+ */
+struct io_pgtable_init_fns {
+ enum io_pgtable_fmt fmt;
+ struct io_pgtable *(*alloc)(struct io_pgtable_cfg *cfg, void *cookie);
+ void (*free)(struct io_pgtable *iop);
+};
+
+/**
+ * io_pgtable_ops_register() - Register the page table routines for a page table
+ * format.
+ *
+ * @init_fns: The functions for allocating and freeing the page tables of
+ * a particular format.
+ */
+int io_pgtable_ops_register(struct io_pgtable_init_fns *init_fns);
+
+/**
+ * io_pgtable_ops_unregister() - Unregister the page table routines for a page
+ * table format.
+ *
+ * @init_fns: The functions for allocating and freeing the page tables of
+ * a particular format.
+ */
+void io_pgtable_ops_unregister(struct io_pgtable_init_fns *init_fns);
+
+/**
* alloc_io_pgtable_ops() - Allocate a page table allocator for use by an IOMMU.
*
* @fmt: The page table format.
@@ -233,23 +265,4 @@ io_pgtable_tlb_add_page(struct io_pgtable *iop,
iop->cfg.tlb->tlb_add_page(gather, iova, granule, iop->cookie);
}
-/**
- * struct io_pgtable_init_fns - Alloc/free a set of page tables for a
- * particular format.
- *
- * @alloc: Allocate a set of page tables described by cfg.
- * @free: Free the page tables associated with iop.
- */
-struct io_pgtable_init_fns {
- struct io_pgtable *(*alloc)(struct io_pgtable_cfg *cfg, void *cookie);
- void (*free)(struct io_pgtable *iop);
-};
-
-extern struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s1_init_fns;
-extern struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns;
-extern struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s1_init_fns;
-extern struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns;
-extern struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns;
-extern struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns;
-
#endif /* __IO_PGTABLE_H */