[Bug 104708] [IGT] igt at gem_exec_flush@* BUG: unable to handle kernel paging request at 0000000100000084

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104708

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #16 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit 77dfedb5be03779f9a5d83e323a1b36e32090105
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri May 11 13:11:45 2018 +0100

    drm/i915/execlists: Use rmb() to order CSB reads

    We assume that the CSB is written using the normal ringbuffer
    coherency protocols, as outlined in kernel/events/ring_buffer.c:

        *   (HW)                              (DRIVER)
        *
        *   if (LOAD ->data_tail) {            LOAD ->data_head
        *                      (A)             smp_rmb()       (C)
        *      STORE $data                     LOAD $data
        *      smp_wmb()       (B)             smp_mb()        (D)
        *      STORE ->data_head               STORE ->data_tail
        *   }

    So we assume that the HW fulfils its ordering requirements (B), and so
    we should use a complimentary rmb (C) to ensure that our read of its
    WRITE pointer is completed before we start accessing the data.

    The final mb (D) is implied by the uncached mmio we perform to inform
    the HW of our READ pointer.

    References: https://bugs.freedesktop.org/show_bug.cgi?id=105064
    References: https://bugs.freedesktop.org/show_bug.cgi?id=105888
    References: https://bugs.freedesktop.org/show_bug.cgi?id=106185
    Fixes: 767a983ab255 ("drm/i915/execlists: Read the context-status HEAD from
the HWSP")
    References: 61bf9719fa17 ("drm/i915/cnl: Use mmio access to context status
buffer")
    Suggested-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
    Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Cc: Michał Winiarski <michal.winiarski at intel.com>
    Cc: Rafael Antognolli <rafael.antognolli at intel.com>
    Cc: Michel Thierry <michel.thierry at intel.com>
    Cc: Timo Aaltonen <tjaalton at ubuntu.com>
    Tested-by: Timo Aaltonen <tjaalton at ubuntu.com>
    Acked-by: Michel Thierry <michel.thierry at intel.com>
    Acked-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20180511121147.31915-1-chris@chris-wilson.co.uk

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