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    Subject[PATCH v2 4/5] powerpc/fault: Perform exception fixup in do_page_fault()
    Date
    Exception fixup doesn't require the heady full regs saving,
    do it from do_page_fault() directly.

    For that, split bad_page_fault() in two parts.

    As bad_page_fault() can also be called from other places than
    handle_page_fault(), it will still perform exception fixup and
    fallback on __bad_page_fault().

    handle_page_fault() directly calls __bad_page_fault() as the
    exception fixup will now be done by do_page_fault()

    Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
    Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
    ---
    v2: Add prototype of __bad_page_fault() in asm/bug.h
    ---
    arch/powerpc/include/asm/bug.h | 1 +
    arch/powerpc/kernel/entry_32.S | 2 +-
    arch/powerpc/kernel/exceptions-64e.S | 2 +-
    arch/powerpc/kernel/exceptions-64s.S | 2 +-
    arch/powerpc/mm/fault.c | 33 ++++++++++++++++++++--------
    5 files changed, 28 insertions(+), 12 deletions(-)

    diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
    index 338f36cd9934..919a31840e51 100644
    --- a/arch/powerpc/include/asm/bug.h
    +++ b/arch/powerpc/include/asm/bug.h
    @@ -113,6 +113,7 @@
    struct pt_regs;
    extern int do_page_fault(struct pt_regs *, unsigned long, unsigned long);
    extern void bad_page_fault(struct pt_regs *, unsigned long, int);
    +void __bad_page_fault(struct pt_regs *regs, unsigned long address, int sig);
    extern void _exception(int, struct pt_regs *, int, unsigned long);
    extern void _exception_pkey(struct pt_regs *, unsigned long, int);
    extern void die(const char *, struct pt_regs *, long);
    diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
    index 8cdc8bcde703..eafcf43e3613 100644
    --- a/arch/powerpc/kernel/entry_32.S
    +++ b/arch/powerpc/kernel/entry_32.S
    @@ -671,7 +671,7 @@ handle_page_fault:
    mr r5,r3
    addi r3,r1,STACK_FRAME_OVERHEAD
    lwz r4,_DAR(r1)
    - bl bad_page_fault
    + bl __bad_page_fault
    b ret_from_except_full

    #ifdef CONFIG_PPC_BOOK3S_32
    diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
    index f579ce46eef2..74d07dc0bb48 100644
    --- a/arch/powerpc/kernel/exceptions-64e.S
    +++ b/arch/powerpc/kernel/exceptions-64e.S
    @@ -1023,7 +1023,7 @@ storage_fault_common:
    mr r5,r3
    addi r3,r1,STACK_FRAME_OVERHEAD
    ld r4,_DAR(r1)
    - bl bad_page_fault
    + bl __bad_page_fault
    b ret_from_except

    /*
    diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
    index f7d748b88705..2cb3bcfb896d 100644
    --- a/arch/powerpc/kernel/exceptions-64s.S
    +++ b/arch/powerpc/kernel/exceptions-64s.S
    @@ -3254,7 +3254,7 @@ handle_page_fault:
    mr r5,r3
    addi r3,r1,STACK_FRAME_OVERHEAD
    ld r4,_DAR(r1)
    - bl bad_page_fault
    + bl __bad_page_fault
    b interrupt_return

    /* We have a data breakpoint exception - handle it */
    diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
    index 1770b41e4730..2e50bc1c3783 100644
    --- a/arch/powerpc/mm/fault.c
    +++ b/arch/powerpc/mm/fault.c
    @@ -538,10 +538,20 @@ NOKPROBE_SYMBOL(__do_page_fault);
    int do_page_fault(struct pt_regs *regs, unsigned long address,
    unsigned long error_code)
    {
    + const struct exception_table_entry *entry;
    enum ctx_state prev_state = exception_enter();
    int rc = __do_page_fault(regs, address, error_code);
    exception_exit(prev_state);
    - return rc;
    + if (likely(!rc))
    + return 0;
    +
    + entry = search_exception_tables(regs->nip);
    + if (unlikely(!entry))
    + return rc;
    +
    + instruction_pointer_set(regs, extable_fixup(entry));
    +
    + return 0;
    }
    NOKPROBE_SYMBOL(do_page_fault);

    @@ -550,17 +560,10 @@ NOKPROBE_SYMBOL(do_page_fault);
    * It is called from the DSI and ISI handlers in head.S and from some
    * of the procedures in traps.c.
    */
    -void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
    +void __bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
    {
    - const struct exception_table_entry *entry;
    int is_write = page_fault_is_write(regs->dsisr);

    - /* Are we prepared to handle this fault? */
    - if ((entry = search_exception_tables(regs->nip)) != NULL) {
    - regs->nip = extable_fixup(entry);
    - return;
    - }
    -
    /* kernel has accessed a bad area */

    switch (TRAP(regs)) {
    @@ -594,3 +597,15 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)

    die("Kernel access of bad area", regs, sig);
    }
    +
    +void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
    +{
    + const struct exception_table_entry *entry;
    +
    + /* Are we prepared to handle this fault? */
    + entry = search_exception_tables(instruction_pointer(regs));
    + if (entry)
    + instruction_pointer_set(regs, extable_fixup(entry));
    + else
    + __bad_page_fault(regs, address, sig);
    +}
    --
    2.25.0
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