Re: [PATCH v4 1/6] drm/i915/gen8: Add infrastructure to initialize WA batch buffers

Chris Wilson
2015-06-16T20:25:38Z

On Tue, Jun 16, 2015 at 08:25:20PM +0100, Arun Siluvery wrote:
> +static int gen8_init_indirectctx_bb(struct intel_engine_cs *ring,
> + uint32_t offset,
> + uint32_t *num_dwords)
> +{
> + uint32_t index;
> + struct page *page;
> + uint32_t *cmd;
> +
> + page = i915_gem_object_get_page(ring->wa_ctx.obj, 0);
> + cmd = kmap_atomic(page);
> +
> + index = offset;
> +
> + /* FIXME: fill one cacheline with NOOPs.
> + * Replace these instructions with WA
> + */
> + while (index < (offset + 16))
> + cmd[index++] = MI_NOOP;
> +
> + /*
> + * MI_BATCH_BUFFER_END is not required in Indirect ctx BB because
> + * execution depends on the length specified in terms of cache lines
> + * in the register CTX_RCS_INDIRECT_CTX
> + */
> +
> + kunmap_atomic(cmd);
> +
> + if (index > (PAGE_SIZE / sizeof(uint32_t)))
> + return -EINVAL;

Check before you GPF!

You just overran the buffer and corrupted memory, if you didn't succeed
in trapping a segfault.

To be generic, align to the cacheline then check you have enough room
for your own data.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre