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

[Souptick Joarder]

On Sat, Nov 3, 2018 at 10:31 AM 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.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> ---
>  include/linux/mm.h       | 46 -----------------------------
>  include/linux/mm_types.h | 75 +++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 74 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..48c2108 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 +608,80 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
>
>  struct vm_fault;
>
> +/**
> + * typedef vm_fault_t -  __bitwise unsigned int
> + *
> + * vm_fault_t is the new unsigned int type to return VM_FAULT
> + * code by page fault handlers of drivers/file systems. Now if
> + * any page fault handlers returns non VM_FAULT code instead
> + * of VM_FAULT code, it will be a mismatch with function
> + * prototype and sparse will detect it.
> + */
> +typedef __bitwise unsigned int vm_fault_t;
> +
> +/**
> + * enum - VM_FAULT code
> + *
> + * This enum is used to track the VM_FAULT code return by page
> + * fault handlers.
> + *
> + * @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)
> + */
> +enum {
> +       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" }
> +

checkpatch.pl is throwing an error "ERROR: Macros with complex values
should be enclosed in parentheses". But if I put it under macro it leads to
compile error for * make allyesconfig * ( x86_64 arch).
That the reason I have ignored the error in checkpatch.pl.

>  struct vm_special_mapping {
>         const char *name;       /* The name, e.g. "[vdso]". */
>
> --
> 1.9.1
>