[PATCH v2] drm/xe/oa: Fix overflow in oa batch buffer

[Dixit, Ashutosh]

On Thu, 12 Sep 2024 08:38:42 -0700, José Roberto de Souza wrote:
>
> By default xe_bb_create_job() appends a MI_BATCH_BUFFER_END to batch
> buffer, this is not a problem if batch buffer is only used once but
> oa reuses the batch buffer for the same metric and at each call
> it appends a MI_BATCH_BUFFER_END, printing the warning below and then
> overflowing.
>
> [  381.072016] ------------[ cut here ]------------
> [  381.072019] xe 0000:00:02.0: [drm] Assertion `bb->len * 4 + bb_prefetch(q->gt) <= size` failed!

I'd think just this one line from this log is sufficient for the commit message.

>                platform: LUNARLAKE subplatform: 1
>                graphics: Xe2_LPG / Xe2_HPG 20.04 step B0
>                media: Xe2_LPM / Xe2_HPM 20.00 step B0
>                tile: 0 VRAM 0 B
>                GT: 0 type 1
>
> So here checking if batch buffer already have MI_BATCH_BUFFER_END if
> not append it.
>
> v2:
> - simply fix, suggestion from Ashutosh
>
> Cc: Ashutosh Dixit <ashutosh.dixit at intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_bb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_bb.c b/drivers/gpu/drm/xe/xe_bb.c
> index a13e0b3a169ed..ef777dbdf4ecc 100644
> --- a/drivers/gpu/drm/xe/xe_bb.c
> +++ b/drivers/gpu/drm/xe/xe_bb.c
> @@ -65,7 +65,8 @@ __xe_bb_create_job(struct xe_exec_queue *q, struct xe_bb *bb, u64 *addr)
>  {
>	u32 size = drm_suballoc_size(bb->bo);
>
> -	bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
> +	if (bb->len == 0 || bb->cs[bb->len - 1] != MI_BATCH_BUFFER_END)
> +		bb->cs[bb->len++] = MI_BATCH_BUFFER_END;

In any case, thanks for the fix:

Reviewed-by: Ashutosh Dixit <ashutosh.dixit at intel.com>

>	xe_gt_assert(q->gt, bb->len * 4 + bb_prefetch(q->gt) <= size);
>
> --
> 2.46.0
>