[PATCH v2 2/4] drivers/iommu: Add calls for IOMMU_DEBUG_PAGEALLOC

Mostafa Saleh
2025-11-06T16:40:12Z

Add calls for the new iommu debug config IOMMU_DEBUG_PAGEALLOC:
- iommu_debug_init: Enable the debug mode if configured by the user.
- iommu_debug_map: Track iommu pages mapped, using physical address.
- iommu_debug_unmap: Track iommu pages unmapped, using IO virtual
address.
- iommu_debug_remap: Track iommu pages, already mapped using IOVA.

We have to do the unmap/remap as once pages are unmapped we lose the
information of the physical address.
This is racy, but the API is racy by construction as it uses refcounts
and doesn't attempt to lock/synchronize with the IOMMU API as that will
be costly, meaning that possibility of false negative exists.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
Tested-by: Qinxin Xia <xiaqinxin@huawei.com>
---
drivers/iommu/iommu-debug-pagealloc.c | 23 ++++++++++++
drivers/iommu/iommu.c | 14 ++++++-
include/linux/iommu-debug-pagealloc.h | 54 +++++++++++++++++++++++++++
3 files changed, 89 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
index 385c8bfae02b..a6a2f844b09d 100644
--- a/drivers/iommu/iommu-debug-pagealloc.c
+++ b/drivers/iommu/iommu-debug-pagealloc.c
@@ -5,11 +5,13 @@
* IOMMU API debug page alloc sanitizer
*/
#include <linux/atomic.h>
+#include <linux/iommu.h>
#include <linux/iommu-debug-pagealloc.h>
#include <linux/kernel.h>
#include <linux/page_ext.h>

static bool needed;
+DEFINE_STATIC_KEY_FALSE(iommu_debug_initialized);

struct iommu_debug_metadate {
atomic_t ref;
@@ -25,6 +27,27 @@ struct page_ext_operations page_iommu_debug_ops = {
.need = need_iommu_debug,
};

+void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
+{
+}
+
+void __iommu_debug_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
+{
+}
+
+void __iommu_debug_remap(struct iommu_domain *domain, unsigned long iova, size_t size)
+{
+}
+
+void iommu_debug_init(void)
+{
+ if (!needed)
+ return;
+
+ pr_info("iommu: Debugging page allocations, expect overhead or disable iommu.debug_pagealloc");
+ static_branch_enable(&iommu_debug_initialized);
+}
+
static int __init iommu_debug_pagealloc(char *str)
{
return kstrtobool(str, &needed);
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 59244c744eab..f374ac0fdf95 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -18,6 +18,7 @@
#include <linux/errno.h>
#include <linux/host1x_context_bus.h>
#include <linux/iommu.h>
+#include <linux/iommu-debug-pagealloc.h>
#include <linux/iommufd.h>
#include <linux/idr.h>
#include <linux/err.h>
@@ -231,6 +232,8 @@ static int __init iommu_subsys_init(void)
if (!nb)
return -ENOMEM;

+ iommu_debug_init();
+
for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++) {
nb[i].notifier_call = iommu_bus_notifier;
bus_register_notifier(iommu_buses[i], &nb[i]);
@@ -2544,10 +2547,12 @@ int iommu_map_nosync(struct iommu_domain *domain, unsigned long iova,
}

/* unroll mapping in case something went wrong */
- if (ret)
+ if (ret) {
iommu_unmap(domain, orig_iova, orig_size - size);
- else
+ } else {
trace_map(orig_iova, orig_paddr, orig_size);
+ iommu_debug_map(domain, orig_paddr, orig_size);
+ }

return ret;
}
@@ -2609,6 +2614,8 @@ static size_t __iommu_unmap(struct iommu_domain *domain,

pr_debug("unmap this: iova 0x%lx size 0x%zx\n", iova, size);

+ iommu_debug_unmap(domain, iova, size);
+
/*
* Keep iterating until we either unmap 'size' bytes (or more)
* or we hit an area that isn't mapped.
@@ -2628,6 +2635,9 @@ static size_t __iommu_unmap(struct iommu_domain *domain,
unmapped += unmapped_page;
}

+ if (unmapped < size)
+ iommu_debug_remap(domain, iova, size - unmapped);
+
trace_unmap(orig_iova, size, unmapped);
return unmapped;
}
diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
index 83e64d70bf6c..180446d6d86f 100644
--- a/include/linux/iommu-debug-pagealloc.h
+++ b/include/linux/iommu-debug-pagealloc.h
@@ -8,10 +8,64 @@
#ifndef __LINUX_IOMMU_DEBUG_PAGEALLOC_H
#define __LINUX_IOMMU_DEBUG_PAGEALLOC_H

+struct iommu_domain;
+
#ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC

+DECLARE_STATIC_KEY_FALSE(iommu_debug_initialized);
+
extern struct page_ext_operations page_iommu_debug_ops;

+void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys,
+ size_t size);
+void __iommu_debug_unmap(struct iommu_domain *domain, unsigned long iova,
+ size_t size);
+void __iommu_debug_remap(struct iommu_domain *domain, unsigned long iova,
+ size_t size);
+
+static inline void iommu_debug_map(struct iommu_domain *domain,
+ phys_addr_t phys, size_t size)
+{
+ if (static_branch_unlikely(&iommu_debug_initialized))
+ __iommu_debug_map(domain, phys, size);
+}
+
+static inline void iommu_debug_unmap(struct iommu_domain *domain,
+ unsigned long iova, size_t size)
+{
+ if (static_branch_unlikely(&iommu_debug_initialized))
+ __iommu_debug_unmap(domain, iova, size);
+}
+
+static inline void iommu_debug_remap(struct iommu_domain *domain,
+ unsigned long iova, size_t size)
+{
+ if (static_branch_unlikely(&iommu_debug_initialized))
+ __iommu_debug_remap(domain, iova, size);
+}
+
+void iommu_debug_init(void);
+
+#else
+static inline void iommu_debug_map(struct iommu_domain *domain,
+ phys_addr_t phys, size_t size)
+{
+}
+
+static inline void iommu_debug_unmap(struct iommu_domain *domain,
+ unsigned long iova, size_t size)
+{
+}
+
+static inline void iommu_debug_remap(struct iommu_domain *domain,
+ unsigned long iova, size_t size)
+{
+}
+
+static inline void iommu_debug_init(void)
+{
+}
+
#endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */

#endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
--
2.51.2.1026.g39e6a42477-goog