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Subject[PATCH] mm/hmm: Fix memremap.h, move dev_page_fault_t callback to hmm
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Date
The kbuild robot reported the following on a development branch that
used memremap.h in a new path:

In file included from arch/m68k/include/asm/pgtable_mm.h:148:0,
from arch/m68k/include/asm/pgtable.h:5,
from include/linux/memremap.h:7,
from drivers//dax/bus.c:3:
arch/m68k/include/asm/motorola_pgtable.h: In function 'pgd_offset':
>> arch/m68k/include/asm/motorola_pgtable.h:199:11: error: dereferencing pointer to incomplete type 'const struct mm_struct'
return mm->pgd + pgd_index(address);
^~

The ->page_fault() callback is specific to HMM. Move it to 'struct
hmm_devmem' where the unusual asm/pgtable.h dependency can be contained
in include/linux/hmm.h. Longer term refactoring this dependency out of
HMM is recommended, but in the meantime memremap.h remains generic.

Fixes: 5042db43cc26 "mm/ZONE_DEVICE: new type of ZONE_DEVICE memory..."
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Hi Andrew, a fairly straightfoward fix, hopefully Jérôme has time to ack
it before the holidays.

It has been exposed to 0day for a few hours with no reported compile
breakage.

include/linux/hmm.h | 24 ++++++++++++++++++++++++
include/linux/memremap.h | 32 --------------------------------
kernel/memremap.c | 6 +++++-
mm/hmm.c | 4 ++--
4 files changed, 31 insertions(+), 35 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index ed89fbc525d2..66f9ebbb1df3 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -69,6 +69,7 @@
#define LINUX_HMM_H

#include <linux/kconfig.h>
+#include <asm/pgtable.h>

#if IS_ENABLED(CONFIG_HMM)

@@ -486,6 +487,7 @@ struct hmm_devmem_ops {
* @device: device to bind resource to
* @ops: memory operations callback
* @ref: per CPU refcount
+ * @page_fault: callback when CPU fault on an unaddressable device page
*
* This an helper structure for device drivers that do not wish to implement
* the gory details related to hotplugging new memoy and allocating struct
@@ -493,7 +495,28 @@ struct hmm_devmem_ops {
*
* Device drivers can directly use ZONE_DEVICE memory on their own if they
* wish to do so.
+ *
+ * The page_fault() callback must migrate page back, from device memory to
+ * system memory, so that the CPU can access it. This might fail for various
+ * reasons (device issues, device have been unplugged, ...). When such error
+ * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and
+ * set the CPU page table entry to "poisoned".
+ *
+ * Note that because memory cgroup charges are transferred to the device memory,
+ * this should never fail due to memory restrictions. However, allocation
+ * of a regular system page might still fail because we are out of memory. If
+ * that happens, the page_fault() callback must return VM_FAULT_OOM.
+ *
+ * The page_fault() callback can also try to migrate back multiple pages in one
+ * chunk, as an optimization. It must, however, prioritize the faulting address
+ * over all the others.
*/
+typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
+ unsigned long addr,
+ const struct page *page,
+ unsigned int flags,
+ pmd_t *pmdp);
+
struct hmm_devmem {
struct completion completion;
unsigned long pfn_first;
@@ -503,6 +526,7 @@ struct hmm_devmem {
struct dev_pagemap pagemap;
const struct hmm_devmem_ops *ops;
struct percpu_ref ref;
+ dev_page_fault_t page_fault;
};

/*
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 55db66b3716f..f0628660d541 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -4,8 +4,6 @@
#include <linux/ioport.h>
#include <linux/percpu-refcount.h>

-#include <asm/pgtable.h>
-
struct resource;
struct device;

@@ -66,47 +64,18 @@ enum memory_type {
};

/*
- * For MEMORY_DEVICE_PRIVATE we use ZONE_DEVICE and extend it with two
- * callbacks:
- * page_fault()
- * page_free()
- *
* Additional notes about MEMORY_DEVICE_PRIVATE may be found in
* include/linux/hmm.h and Documentation/vm/hmm.rst. There is also a brief
* explanation in include/linux/memory_hotplug.h.
*
- * The page_fault() callback must migrate page back, from device memory to
- * system memory, so that the CPU can access it. This might fail for various
- * reasons (device issues, device have been unplugged, ...). When such error
- * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and
- * set the CPU page table entry to "poisoned".
- *
- * Note that because memory cgroup charges are transferred to the device memory,
- * this should never fail due to memory restrictions. However, allocation
- * of a regular system page might still fail because we are out of memory. If
- * that happens, the page_fault() callback must return VM_FAULT_OOM.
- *
- * The page_fault() callback can also try to migrate back multiple pages in one
- * chunk, as an optimization. It must, however, prioritize the faulting address
- * over all the others.
- *
- *
* The page_free() callback is called once the page refcount reaches 1
* (ZONE_DEVICE pages never reach 0 refcount unless there is a refcount bug.
* This allows the device driver to implement its own memory management.)
- *
- * For MEMORY_DEVICE_PUBLIC only the page_free() callback matter.
*/
-typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
- unsigned long addr,
- const struct page *page,
- unsigned int flags,
- pmd_t *pmdp);
typedef void (*dev_page_free_t)(struct page *page, void *data);

/**
* struct dev_pagemap - metadata for ZONE_DEVICE mappings
- * @page_fault: callback when CPU fault on an unaddressable device page
* @page_free: free page callback when page refcount reaches 1
* @altmap: pre-allocated/reserved memory for vmemmap allocations
* @res: physical address range covered by @ref
@@ -117,7 +86,6 @@ typedef void (*dev_page_free_t)(struct page *page, void *data);
* @type: memory type: see MEMORY_* in memory_hotplug.h
*/
struct dev_pagemap {
- dev_page_fault_t page_fault;
dev_page_free_t page_free;
struct vmem_altmap altmap;
bool altmap_valid;
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 66cbf334203b..f458b44303c9 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -11,6 +11,7 @@
#include <linux/types.h>
#include <linux/wait_bit.h>
#include <linux/xarray.h>
+#include <linux/hmm.h>

static DEFINE_XARRAY(pgmap_array);
#define SECTION_MASK ~((1UL << PA_SECTION_SHIFT) - 1)
@@ -24,6 +25,9 @@ vm_fault_t device_private_entry_fault(struct vm_area_struct *vma,
pmd_t *pmdp)
{
struct page *page = device_private_entry_to_page(entry);
+ struct hmm_devmem *devmem;
+
+ devmem = container_of(page->pgmap, typeof(*devmem), pagemap);

/*
* The page_fault() callback must migrate page back to system memory
@@ -39,7 +43,7 @@ vm_fault_t device_private_entry_fault(struct vm_area_struct *vma,
* There is a more in-depth description of what that callback can and
* cannot do, in include/linux/memremap.h
*/
- return page->pgmap->page_fault(vma, addr, page, flags, pmdp);
+ return devmem->page_fault(vma, addr, page, flags, pmdp);
}
EXPORT_SYMBOL(device_private_entry_fault);
#endif /* CONFIG_DEVICE_PRIVATE */
diff --git a/mm/hmm.c b/mm/hmm.c
index 789587731217..a04e4b810610 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -1087,10 +1087,10 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
devmem->pfn_last = devmem->pfn_first +
(resource_size(devmem->resource) >> PAGE_SHIFT);
+ devmem->page_fault = hmm_devmem_fault;

devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
devmem->pagemap.res = *devmem->resource;
- devmem->pagemap.page_fault = hmm_devmem_fault;
devmem->pagemap.page_free = hmm_devmem_free;
devmem->pagemap.altmap_valid = false;
devmem->pagemap.ref = &devmem->ref;
@@ -1141,10 +1141,10 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
devmem->pfn_last = devmem->pfn_first +
(resource_size(devmem->resource) >> PAGE_SHIFT);
+ devmem->page_fault = hmm_devmem_fault;

devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
devmem->pagemap.res = *devmem->resource;
- devmem->pagemap.page_fault = hmm_devmem_fault;
devmem->pagemap.page_free = hmm_devmem_free;
devmem->pagemap.altmap_valid = false;
devmem->pagemap.ref = &devmem->ref;
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