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Date: Thu, 20 Dec 2018 20:45:30 -0500
From: Jerome Glisse <jglisse@...hat.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: akpm@...ux-foundation.org, Logan Gunthorpe <logang@...tatee.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hmm: Fix memremap.h, move dev_page_fault_t callback
to hmm
On Thu, Dec 20, 2018 at 01:24:13PM -0800, Dan Williams wrote:
> 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..."
Reviewed-by: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.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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