• Vineet Gupta's avatar
    ARCv2: STAR 9000950267: Handle return from intr to Delay Slot #2 · cbfe74a7
    Vineet Gupta authored
    Returning to delay slot, riding an interrupti, had one loose end.
    AUX_USER_SP used for restoring user mode SP upon RTIE was not being
    setup from orig task's saved value, causing task to use wrong SP,
    leading to ProtV errors.
    
    The reason being:
     - INTERRUPT_EPILOGUE returns to a kernel trampoline, thus not expected to restore it
     - EXCEPTION_EPILOGUE is not used at all
    
    Fix that by restoring AUX_USER_SP explicitly in the trampoline.
    
    This was broken in the original workaround, but the error scenarios got
    reduced considerably since v3.14 due to following:
    
     1. The Linuxthreads.old based userspace at the time caused many more
        exceptions in delay slot than the current NPTL based one.
        Infact with current userspace the error doesn't happen at all.
    
     2. Return from interrupt (delay slot or otherwise) doesn't get exercised much
        after commit 4de0e528 ("Really Re-enable interrupts to avoid deadlocks")
        since IRQ_ACTIVE.active being clear means most returns are as if from pure
        kernel (even for active interrupts)
    
    Infact the issue only happened in an experimental branch where I was tinkering with
    reverted 4de0e528
    
    Cc: stable@kernel.org # v4.2+
    Fixes: 4255b07f ("ARCv2: STAR 9000793984: Handle return from intr to Delay Slot")
    Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
    cbfe74a7
entry-arcv2.S 6.49 KB