Re: [PATCH v3] mm: Create the new vm_fault_t type

From: Souptick Joarder
Date: Wed Nov 14 2018 - 00:15:02 EST

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On Tue, Nov 6, 2018 at 5:33 PM Souptick Joarder <jrdr.linux@xxxxxxxxx> wrote:
>
> Page fault handlers are supposed to return VM_FAULT codes,
> but some drivers/file systems mistakenly return error
> numbers. Now that all drivers/file systems have been converted
> to use the vm_fault_t return type, change the type definition
> to no longer be compatible with 'int'. By making it an unsigned
> int, the function prototype becomes incompatible with a function
> which returns int. Sparse will detect any attempts to return a
> value which is not a VM_FAULT code.
>
> VM_FAULT_SET_HINDEX and VM_FAULT_GET_HINDEX values are changed
> to avoid conflict with other VM_FAULT codes.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>

Any further comment on this patch ?
> ---
> v2: Updated the change log and corrected the document part.
> name added to the enum that kernel-doc able to parse it.
>
> v3: Corrected the documentation.
>
> include/linux/mm.h | 46 ------------------------------
> include/linux/mm_types.h | 73 +++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 72 insertions(+), 47 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index fcf9cc9..511a3ce 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1267,52 +1267,6 @@ static inline void clear_page_pfmemalloc(struct page *page)
> }
>
> /*
> - * Different kinds of faults, as returned by handle_mm_fault().
> - * Used to decide whether a process gets delivered SIGBUS or
> - * just gets major/minor fault counters bumped up.
> - */
> -
> -#define VM_FAULT_OOM 0x0001
> -#define VM_FAULT_SIGBUS 0x0002
> -#define VM_FAULT_MAJOR 0x0004
> -#define VM_FAULT_WRITE 0x0008 /* Special case for get_user_pages */
> -#define VM_FAULT_HWPOISON 0x0010 /* Hit poisoned small page */
> -#define VM_FAULT_HWPOISON_LARGE 0x0020 /* Hit poisoned large page. Index encoded in upper bits */
> -#define VM_FAULT_SIGSEGV 0x0040
> -
> -#define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page */
> -#define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
> -#define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */
> -#define VM_FAULT_FALLBACK 0x0800 /* huge page fault failed, fall back to small */
> -#define VM_FAULT_DONE_COW 0x1000 /* ->fault has fully handled COW */
> -#define VM_FAULT_NEEDDSYNC 0x2000 /* ->fault did not modify page tables
> - * and needs fsync() to complete (for
> - * synchronous page faults in DAX) */
> -
> -#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
> - VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
> - VM_FAULT_FALLBACK)
> -
> -#define VM_FAULT_RESULT_TRACE \
> - { VM_FAULT_OOM, "OOM" }, \
> - { VM_FAULT_SIGBUS, "SIGBUS" }, \
> - { VM_FAULT_MAJOR, "MAJOR" }, \
> - { VM_FAULT_WRITE, "WRITE" }, \
> - { VM_FAULT_HWPOISON, "HWPOISON" }, \
> - { VM_FAULT_HWPOISON_LARGE, "HWPOISON_LARGE" }, \
> - { VM_FAULT_SIGSEGV, "SIGSEGV" }, \
> - { VM_FAULT_NOPAGE, "NOPAGE" }, \
> - { VM_FAULT_LOCKED, "LOCKED" }, \
> - { VM_FAULT_RETRY, "RETRY" }, \
> - { VM_FAULT_FALLBACK, "FALLBACK" }, \
> - { VM_FAULT_DONE_COW, "DONE_COW" }, \
> - { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }
> -
> -/* Encode hstate index for a hwpoisoned large page */
> -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> -
> -/*
> * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
> */
> extern void pagefault_out_of_memory(void);
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5ed8f62..cb25016 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -22,7 +22,6 @@
> #endif
> #define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))
>
> -typedef int vm_fault_t;
>
> struct address_space;
> struct mem_cgroup;
> @@ -609,6 +608,78 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
>
> struct vm_fault;
>
> +/**
> + * typedef vm_fault_t - Return type for page fault handlers.
> + *
> + * Page fault handlers return a bitmask of %VM_FAULT values.
> + */
> +typedef __bitwise unsigned int vm_fault_t;
> +
> +/**
> + * enum vm_fault_reason - Page fault handlers return a bitmask of
> + * these values to tell the core VM what happened when handling the
> + * fault. Used to decide whether a process gets delivered SIGBUS or
> + * just gets major/minor fault counters bumped up.
> + *
> + * @VM_FAULT_OOM: Out Of Memory
> + * @VM_FAULT_SIGBUS: Bad access
> + * @VM_FAULT_MAJOR: Page read from storage
> + * @VM_FAULT_WRITE: Special case for get_user_pages
> + * @VM_FAULT_HWPOISON: Hit poisoned small page
> + * @VM_FAULT_HWPOISON_LARGE: Hit poisoned large page. Index encoded
> + * in upper bits
> + * @VM_FAULT_SIGSEGV: segmentation fault
> + * @VM_FAULT_NOPAGE: ->fault installed the pte, not return page
> + * @VM_FAULT_LOCKED: ->fault locked the returned page
> + * @VM_FAULT_RETRY: ->fault blocked, must retry
> + * @VM_FAULT_FALLBACK: huge page fault failed, fall back to small
> + * @VM_FAULT_DONE_COW: ->fault has fully handled COW
> + * @VM_FAULT_NEEDDSYNC: ->fault did not modify page tables and needs
> + * fsync() to complete (for synchronous page faults
> + * in DAX)
> + * @VM_FAULT_HINDEX_MASK: mask HINDEX value
> + *
> + */
> +enum vm_fault_reason {
> + VM_FAULT_OOM = (__force vm_fault_t)0x000001,
> + VM_FAULT_SIGBUS = (__force vm_fault_t)0x000002,
> + VM_FAULT_MAJOR = (__force vm_fault_t)0x000004,
> + VM_FAULT_WRITE = (__force vm_fault_t)0x000008,
> + VM_FAULT_HWPOISON = (__force vm_fault_t)0x000010,
> + VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
> + VM_FAULT_SIGSEGV = (__force vm_fault_t)0x000040,
> + VM_FAULT_NOPAGE = (__force vm_fault_t)0x000100,
> + VM_FAULT_LOCKED = (__force vm_fault_t)0x000200,
> + VM_FAULT_RETRY = (__force vm_fault_t)0x000400,
> + VM_FAULT_FALLBACK = (__force vm_fault_t)0x000800,
> + VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000,
> + VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000,
> + VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000,
> +};
> +
> +/* Encode hstate index for a hwpoisoned large page */
> +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> +
> +#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | \
> + VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON | \
> + VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)
> +
> +#define VM_FAULT_RESULT_TRACE \
> + { VM_FAULT_OOM, "OOM" }, \
> + { VM_FAULT_SIGBUS, "SIGBUS" }, \
> + { VM_FAULT_MAJOR, "MAJOR" }, \
> + { VM_FAULT_WRITE, "WRITE" }, \
> + { VM_FAULT_HWPOISON, "HWPOISON" }, \
> + { VM_FAULT_HWPOISON_LARGE, "HWPOISON_LARGE" }, \
> + { VM_FAULT_SIGSEGV, "SIGSEGV" }, \
> + { VM_FAULT_NOPAGE, "NOPAGE" }, \
> + { VM_FAULT_LOCKED, "LOCKED" }, \
> + { VM_FAULT_RETRY, "RETRY" }, \
> + { VM_FAULT_FALLBACK, "FALLBACK" }, \
> + { VM_FAULT_DONE_COW, "DONE_COW" }, \
> + { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }
> +
> struct vm_special_mapping {
> const char *name; /* The name, e.g. "[vdso]". */
>
> --
> 1.9.1
>

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