[Intel-gfx] [PATCH 02/13] drm/i915: Copy user requested buffers into the error state

[Matt Turner]

On Wed, Mar 29, 2017 at 8:56 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> Introduce a new execobject.flag (EXEC_OBJECT_CAPTURE) that userspace may
> use to indicate that it wants the contents of this buffer preserved in
> the error state (/sys/class/drm/cardN/error) following a GPU hang
> involving this batch.
>
> Use this at your discretion, the contents of the error state. although
> compressed, are allocated with GFP_ATOMIC (i.e. limited) and kept for all
> eternity (until the error state is destroyed).
>
> Based on an earlier patch by Ben Widawsky <ben at bwidawsk.net>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ben Widawsky <ben at bwidawsk.net>
> Cc: Matt Turner <mattst88 at gmail.com>
> Acked-by: Ben Widawsky <ben at bwidawsk.net>
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---

Thank you, Chris. With this in place (and a few patches from Ben
rebased for libdrm and Mesa) I can disassemble the shader program from
an error state.

In this case, I turned off the end-of-thread bit on the sendc in order
to cause a hang:

render ring --- user = 0x00000000 fff75000
pln(8)          g124<1>F        g4<0,1,0>F      g2<8,8,1>F      {
align1 1Q compacted };
pln(8)          g125<1>F        g4.4<0,1,0>F    g2<8,8,1>F      {
align1 1Q compacted };
pln(8)          g126<1>F        g5<0,1,0>F      g2<8,8,1>F      {
align1 1Q compacted };
pln(8)          g127<1>F        g5.4<0,1,0>F    g2<8,8,1>F      {
align1 1Q compacted };
sendc(8)        null<1>UW       g124<8,8,1>F
                            render RT write SIMD8 LastRT Surface = 0
mlen 4 rlen 0 { align1 1Q };
nop                                                             ;
pln(16)         g120<1>F        g6<0,1,0>F      g2<8,8,1>F      {
align1 1H compacted };
pln(16)         g122<1>F        g6.4<0,1,0>F    g2<8,8,1>F      {
align1 1H compacted };
pln(16)         g124<1>F        g7<0,1,0>F      g2<8,8,1>F      {
align1 1H compacted };
pln(16)         g126<1>F        g7.4<0,1,0>F    g2<8,8,1>F      {
align1 1H compacted };
sendc(16)       null<1>UW       g120<8,8,1>F
                            render RT write SIMD16 LastRT Surface = 0
mlen 8 rlen 0 { align1 1H };
illegal(1)                                                      { align1 1N };

Presumably we would like to save more than just instruction buffers.
Do we have a good way of discerning what each blob of data in the
error state is?