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    Subject[PATCH 4.4 25/27] parisc: Avoid trashing sr2 and sr3 in LWS code
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: John David Anglin <dave.anglin@bell.net>

    commit f4125cfdb3008363137f744c101e5d76ead760ba upstream.

    There is no need to trash sr2 and sr3 in the Light-weight syscall (LWS). sr2
    already points to kernel space (it's zero in userspace, otherwise syscalls
    wouldn't work), and since the LWS code is executed in userspace, we can simply
    ignore to preload sr3.

    Signed-off-by: John David Anglin <dave.anglin@bell.net>
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/parisc/kernel/syscall.S | 53 +++++++++++++++++++------------------------
    1 file changed, 24 insertions(+), 29 deletions(-)

    --- a/arch/parisc/kernel/syscall.S
    +++ b/arch/parisc/kernel/syscall.S
    @@ -479,11 +479,6 @@ lws_start:
    comiclr,>> __NR_lws_entries, %r20, %r0
    b,n lws_exit_nosys

    - /* WARNING: Trashing sr2 and sr3 */
    - mfsp %sr7,%r1 /* get userspace into sr3 */
    - mtsp %r1,%sr3
    - mtsp %r0,%sr2 /* get kernel space into sr2 */
    -
    /* Load table start */
    ldil L%lws_table, %r1
    ldo R%lws_table(%r1), %r28 /* Scratch use of r28 */
    @@ -632,9 +627,9 @@ cas_action:
    stw %r1, 4(%sr2,%r20)
    #endif
    /* The load and store could fail */
    -1: ldw,ma 0(%sr3,%r26), %r28
    +1: ldw,ma 0(%r26), %r28
    sub,<> %r28, %r25, %r0
    -2: stw,ma %r24, 0(%sr3,%r26)
    +2: stw,ma %r24, 0(%r26)
    /* Free lock */
    stw,ma %r20, 0(%sr2,%r20)
    #if ENABLE_LWS_DEBUG
    @@ -711,9 +706,9 @@ lws_compare_and_swap_2:
    nop

    /* 8bit load */
    -4: ldb 0(%sr3,%r25), %r25
    +4: ldb 0(%r25), %r25
    b cas2_lock_start
    -5: ldb 0(%sr3,%r24), %r24
    +5: ldb 0(%r24), %r24
    nop
    nop
    nop
    @@ -721,9 +716,9 @@ lws_compare_and_swap_2:
    nop

    /* 16bit load */
    -6: ldh 0(%sr3,%r25), %r25
    +6: ldh 0(%r25), %r25
    b cas2_lock_start
    -7: ldh 0(%sr3,%r24), %r24
    +7: ldh 0(%r24), %r24
    nop
    nop
    nop
    @@ -731,9 +726,9 @@ lws_compare_and_swap_2:
    nop

    /* 32bit load */
    -8: ldw 0(%sr3,%r25), %r25
    +8: ldw 0(%r25), %r25
    b cas2_lock_start
    -9: ldw 0(%sr3,%r24), %r24
    +9: ldw 0(%r24), %r24
    nop
    nop
    nop
    @@ -742,14 +737,14 @@ lws_compare_and_swap_2:

    /* 64bit load */
    #ifdef CONFIG_64BIT
    -10: ldd 0(%sr3,%r25), %r25
    -11: ldd 0(%sr3,%r24), %r24
    +10: ldd 0(%r25), %r25
    +11: ldd 0(%r24), %r24
    #else
    /* Load new value into r22/r23 - high/low */
    -10: ldw 0(%sr3,%r25), %r22
    -11: ldw 4(%sr3,%r25), %r23
    +10: ldw 0(%r25), %r22
    +11: ldw 4(%r25), %r23
    /* Load new value into fr4 for atomic store later */
    -12: flddx 0(%sr3,%r24), %fr4
    +12: flddx 0(%r24), %fr4
    #endif

    cas2_lock_start:
    @@ -799,30 +794,30 @@ cas2_action:
    ldo 1(%r0),%r28

    /* 8bit CAS */
    -13: ldb,ma 0(%sr3,%r26), %r29
    +13: ldb,ma 0(%r26), %r29
    sub,= %r29, %r25, %r0
    b,n cas2_end
    -14: stb,ma %r24, 0(%sr3,%r26)
    +14: stb,ma %r24, 0(%r26)
    b cas2_end
    copy %r0, %r28
    nop
    nop

    /* 16bit CAS */
    -15: ldh,ma 0(%sr3,%r26), %r29
    +15: ldh,ma 0(%r26), %r29
    sub,= %r29, %r25, %r0
    b,n cas2_end
    -16: sth,ma %r24, 0(%sr3,%r26)
    +16: sth,ma %r24, 0(%r26)
    b cas2_end
    copy %r0, %r28
    nop
    nop

    /* 32bit CAS */
    -17: ldw,ma 0(%sr3,%r26), %r29
    +17: ldw,ma 0(%r26), %r29
    sub,= %r29, %r25, %r0
    b,n cas2_end
    -18: stw,ma %r24, 0(%sr3,%r26)
    +18: stw,ma %r24, 0(%r26)
    b cas2_end
    copy %r0, %r28
    nop
    @@ -830,22 +825,22 @@ cas2_action:

    /* 64bit CAS */
    #ifdef CONFIG_64BIT
    -19: ldd,ma 0(%sr3,%r26), %r29
    +19: ldd,ma 0(%r26), %r29
    sub,*= %r29, %r25, %r0
    b,n cas2_end
    -20: std,ma %r24, 0(%sr3,%r26)
    +20: std,ma %r24, 0(%r26)
    copy %r0, %r28
    #else
    /* Compare first word */
    -19: ldw,ma 0(%sr3,%r26), %r29
    +19: ldw,ma 0(%r26), %r29
    sub,= %r29, %r22, %r0
    b,n cas2_end
    /* Compare second word */
    -20: ldw,ma 4(%sr3,%r26), %r29
    +20: ldw,ma 4(%r26), %r29
    sub,= %r29, %r23, %r0
    b,n cas2_end
    /* Perform the store */
    -21: fstdx %fr4, 0(%sr3,%r26)
    +21: fstdx %fr4, 0(%r26)
    copy %r0, %r28
    #endif


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