[Intel-gfx] [PATCH] drm/i915/selftest: Check that GPR are restored across noa_wait

[Lionel Landwerlin]

On 10/07/2020 00:53, Chris Wilson wrote:
> Perf implements a GPU delay (noa_wait) by looping until the CS timestamp
> has passed a certain point. This use MI_MATH and the general purpose
> registers of the user's context, and since it is clobbering the user
> state it must carefully save and restore the user's data around the
> noa_wait. We can verify this by loading some values in the GPR that we
> know will be clobbered the noa_wait, and then inspecting the GPR after
> the noa_wait completes and confirming that have been restored.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>


Thanks a lot!

-Lionel

> ---
>   drivers/gpu/drm/i915/selftests/i915_perf.c | 124 +++++++++++++++++++++
>   1 file changed, 124 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/selftests/i915_perf.c b/drivers/gpu/drm/i915/selftests/i915_perf.c
> index be54570c407c..be63cfe82feb 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_perf.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_perf.c
> @@ -280,11 +280,135 @@ static int live_noa_delay(void *arg)
>   	return err;
>   }
>   
> +static int live_noa_gpr(void *arg)
> +{
> +	struct drm_i915_private *i915 = arg;
> +	struct i915_perf_stream *stream;
> +	struct intel_context *ce;
> +	struct i915_request *rq;
> +	u32 *cs, *store;
> +	void *scratch;
> +	u32 gpr0;
> +	int err;
> +	int i;
> +
> +	/* Check that the delay does not clobber user context state (GPR) */
> +
> +	stream = test_stream(&i915->perf);
> +	if (!stream)
> +		return -ENOMEM;
> +
> +	gpr0 = i915_mmio_reg_offset(GEN8_RING_CS_GPR(stream->engine->mmio_base, 0));
> +
> +	ce = intel_context_create(stream->engine);
> +	if (IS_ERR(ce)) {
> +		err = PTR_ERR(ce);
> +		goto out;
> +	}
> +
> +	scratch = kmap(ce->vm->scratch[0].base.page);
> +	memset(scratch, POISON_FREE, PAGE_SIZE);
> +
> +	rq = intel_context_create_request(ce);
> +	if (IS_ERR(rq)) {
> +		err = PTR_ERR(rq);
> +		goto out_ce;
> +	}
> +	i915_request_get(rq);
> +
> +	if (rq->engine->emit_init_breadcrumb) {
> +		err = rq->engine->emit_init_breadcrumb(rq);
> +		if (err) {
> +			i915_request_add(rq);
> +			goto out_rq;
> +		}
> +	}
> +
> +	cs = intel_ring_begin(rq, 2 * 32 + 2);
> +	if (IS_ERR(cs)) {
> +		i915_request_add(rq);
> +		goto out_rq;
> +	}
> +
> +	*cs++ = MI_LOAD_REGISTER_IMM(32);
> +	for (i = 0; i < 32; i++) {
> +		*cs++ = gpr0 + i * sizeof(u32);
> +		*cs++ = STACK_MAGIC;
> +	}
> +	*cs++ = MI_NOOP;
> +	intel_ring_advance(rq, cs);
> +
> +	err = rq->engine->emit_bb_start(rq,
> +					i915_ggtt_offset(stream->noa_wait), 0,
> +					I915_DISPATCH_SECURE);
> +	if (err) {
> +		i915_request_add(rq);
> +		goto out_rq;
> +	}
> +
> +	store = memset32(rq->engine->status_page.addr + 512, 0, 32);
> +	for (i = 0; i < 32; i++) {
> +		u32 cmd;
> +
> +		cs = intel_ring_begin(rq, 4);
> +		if (IS_ERR(cs)) {
> +			i915_request_add(rq);
> +			goto out_rq;
> +		}
> +
> +		cmd = MI_STORE_REGISTER_MEM;
> +		if (INTEL_GEN(i915) >= 8)
> +			cmd++;
> +		cmd |= MI_USE_GGTT;
> +
> +		*cs++ = cmd;
> +		*cs++ = gpr0 + i * sizeof(u32);
> +		*cs++ = i915_ggtt_offset(rq->engine->status_page.vma) +
> +			offset_in_page(store) +
> +			i * sizeof(u32);
> +		*cs++ = 0;
> +		intel_ring_advance(rq, cs);
> +	}
> +
> +	i915_request_add(rq);
> +
> +	if (i915_request_wait(rq, I915_WAIT_INTERRUPTIBLE, HZ / 2) < 0) {
> +		intel_gt_set_wedged(stream->engine->gt);
> +		err = -EIO;
> +		goto out_rq;
> +	}
> +
> +	for (i = 0; i < 32; i++) {
> +		if (store[i] == STACK_MAGIC)
> +			continue;
> +
> +		pr_err("GPR[%d] lost, found:%08x, expected:%08x!\n",
> +		       i, store[i], STACK_MAGIC);
> +		err = -EINVAL;
> +	}
> +
> +	if (memchr_inv(scratch, POISON_FREE, PAGE_SIZE)) {
> +		pr_err("scratch page overwritten!\n");
> +		igt_hexdump(scratch, 4096);
> +		err = -EINVAL;
> +	}
> +
> +out_rq:
> +	i915_request_put(rq);
> +out_ce:
> +	kunmap(ce->vm->scratch[0].base.page);
> +	intel_context_put(ce);
> +out:
> +	stream_destroy(stream);
> +	return err;
> +}
> +
>   int i915_perf_live_selftests(struct drm_i915_private *i915)
>   {
>   	static const struct i915_subtest tests[] = {
>   		SUBTEST(live_sanitycheck),
>   		SUBTEST(live_noa_delay),
> +		SUBTEST(live_noa_gpr),
>   	};
>   	struct i915_perf *perf = &i915->perf;
>   	int err;