[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

Lakshmi <lakshminarayana.vudum at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #17 from Lakshmi <lakshminarayana.vudum at intel.com> ---
(In reply to Chris Wilson from comment #16)
> 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 at chris-wilson.co.uk

Closing this issue as this was already resolved and verified.

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