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

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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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