From: Chris Wilson chris@chris-wilson.co.uk
commit 8ab3a3812aa90e488813e719308ffd807b865624 upstream.
In commit 5ba32c7be81e ("drm/i915/execlists: Always force a context reload when rewinding RING_TAIL"), we placed the check for rewinding a context on actually submitting the next request in that context. This was so that we only had to check once, and could do so with precision avoiding as many forced restores as possible. For example, to ensure that we can resubmit the same request a couple of times, we include a small wa_tail such that on the next submission, the ring->tail will appear to move forwards when resubmitting the same request. This is very common as it will happen for every lite-restore to fill the second port after a context switch.
However, intel_ring_direction() is limited in precision to movements of upto half the ring size. The consequence being that if we tried to unwind many requests, we could exceed half the ring and flip the sense of the direction, so missing a force restore. As no request can be greater than half the ring (i.e. 2048 bytes in the smallest case), we can check for rollback incrementally. As we check against the tail that would be submitted, we do not lose any sensitivity and allow lite restores for the simple case. We still need to double check upon submitting the context, to allow for multiple preemptions and resubmissions.
Fixes: 5ba32c7be81e ("drm/i915/execlists: Always force a context reload when rewinding RING_TAIL") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Mika Kuoppala mika.kuoppala@linux.intel.com Cc: stable@vger.kernel.org # v5.4+ Reviewed-by: Bruce Chang yu.bruce.chang@intel.com Reviewed-by: Mika Kuoppala mika.kuoppala@linux.intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200609151723.12971-1-chris@c... (cherry picked from commit e36ba817fa966f81fb1c8d16f3721b5a644b2fa9) Signed-off-by: Joonas Lahtinen joonas.lahtinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/gt/intel_engine_cs.c | 4 drivers/gpu/drm/i915/gt/intel_lrc.c | 21 +++ drivers/gpu/drm/i915/gt/intel_ring.c | 4 drivers/gpu/drm/i915/gt/selftest_mocs.c | 18 ++- drivers/gpu/drm/i915/gt/selftest_ring.c | 110 +++++++++++++++++++ drivers/gpu/drm/i915/selftests/i915_mock_selftests.h | 1 6 files changed, 154 insertions(+), 4 deletions(-)
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c @@ -639,7 +639,7 @@ static int engine_setup_common(struct in struct measure_breadcrumb { struct i915_request rq; struct intel_ring ring; - u32 cs[1024]; + u32 cs[2048]; };
static int measure_breadcrumb_dw(struct intel_context *ce) @@ -661,6 +661,8 @@ static int measure_breadcrumb_dw(struct
frame->ring.vaddr = frame->cs; frame->ring.size = sizeof(frame->cs); + frame->ring.wrap = + BITS_PER_TYPE(frame->ring.size) - ilog2(frame->ring.size); frame->ring.effective_size = frame->ring.size; intel_ring_update_space(&frame->ring); frame->rq.ring = &frame->ring; --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -972,6 +972,13 @@ __unwind_incomplete_requests(struct inte list_move(&rq->sched.link, pl); set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
+ /* Check in case we rollback so far we wrap [size/2] */ + if (intel_ring_direction(rq->ring, + intel_ring_wrap(rq->ring, + rq->tail), + rq->ring->tail) > 0) + rq->context->lrc.desc |= CTX_DESC_FORCE_RESTORE; + active = rq; } else { struct intel_engine_cs *owner = rq->context->engine; @@ -1383,8 +1390,9 @@ static u64 execlists_update_context(stru * HW has a tendency to ignore us rewinding the TAIL to the end of * an earlier request. */ + GEM_BUG_ON(ce->lrc_reg_state[CTX_RING_TAIL] != rq->ring->tail); + prev = rq->ring->tail; tail = intel_ring_set_tail(rq->ring, rq->tail); - prev = ce->lrc_reg_state[CTX_RING_TAIL]; if (unlikely(intel_ring_direction(rq->ring, tail, prev) <= 0)) desc |= CTX_DESC_FORCE_RESTORE; ce->lrc_reg_state[CTX_RING_TAIL] = tail; @@ -4213,6 +4221,14 @@ static int gen12_emit_flush_render(struc return 0; }
+static void assert_request_valid(struct i915_request *rq) +{ + struct intel_ring *ring __maybe_unused = rq->ring; + + /* Can we unwind this request without appearing to go forwards? */ + GEM_BUG_ON(intel_ring_direction(ring, rq->wa_tail, rq->head) <= 0); +} + /* * Reserve space for 2 NOOPs at the end of each request to be * used as a workaround for not being allowed to do lite @@ -4225,6 +4241,9 @@ static u32 *gen8_emit_wa_tail(struct i91 *cs++ = MI_NOOP; request->wa_tail = intel_ring_offset(request, cs);
+ /* Check that entire request is less than half the ring */ + assert_request_valid(request); + return cs; }
--- a/drivers/gpu/drm/i915/gt/intel_ring.c +++ b/drivers/gpu/drm/i915/gt/intel_ring.c @@ -315,3 +315,7 @@ int intel_ring_cacheline_align(struct i9 GEM_BUG_ON(rq->ring->emit & (CACHELINE_BYTES - 1)); return 0; } + +#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST) +#include "selftest_ring.c" +#endif --- a/drivers/gpu/drm/i915/gt/selftest_mocs.c +++ b/drivers/gpu/drm/i915/gt/selftest_mocs.c @@ -18,6 +18,20 @@ struct live_mocs { void *vaddr; };
+static struct intel_context *mocs_context_create(struct intel_engine_cs *engine) +{ + struct intel_context *ce; + + ce = intel_context_create(engine); + if (IS_ERR(ce)) + return ce; + + /* We build large requests to read the registers from the ring */ + ce->ring = __intel_context_ring_size(SZ_16K); + + return ce; +} + static int request_add_sync(struct i915_request *rq, int err) { i915_request_get(rq); @@ -301,7 +315,7 @@ static int live_mocs_clean(void *arg) for_each_engine(engine, gt, id) { struct intel_context *ce;
- ce = intel_context_create(engine); + ce = mocs_context_create(engine); if (IS_ERR(ce)) { err = PTR_ERR(ce); break; @@ -395,7 +409,7 @@ static int live_mocs_reset(void *arg) for_each_engine(engine, gt, id) { struct intel_context *ce;
- ce = intel_context_create(engine); + ce = mocs_context_create(engine); if (IS_ERR(ce)) { err = PTR_ERR(ce); break; --- /dev/null +++ b/drivers/gpu/drm/i915/gt/selftest_ring.c @@ -0,0 +1,110 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright © 2020 Intel Corporation + */ + +static struct intel_ring *mock_ring(unsigned long sz) +{ + struct intel_ring *ring; + + ring = kzalloc(sizeof(*ring) + sz, GFP_KERNEL); + if (!ring) + return NULL; + + kref_init(&ring->ref); + ring->size = sz; + ring->wrap = BITS_PER_TYPE(ring->size) - ilog2(sz); + ring->effective_size = sz; + ring->vaddr = (void *)(ring + 1); + atomic_set(&ring->pin_count, 1); + + intel_ring_update_space(ring); + + return ring; +} + +static void mock_ring_free(struct intel_ring *ring) +{ + kfree(ring); +} + +static int check_ring_direction(struct intel_ring *ring, + u32 next, u32 prev, + int expected) +{ + int result; + + result = intel_ring_direction(ring, next, prev); + if (result < 0) + result = -1; + else if (result > 0) + result = 1; + + if (result != expected) { + pr_err("intel_ring_direction(%u, %u):%d != %d\n", + next, prev, result, expected); + return -EINVAL; + } + + return 0; +} + +static int check_ring_step(struct intel_ring *ring, u32 x, u32 step) +{ + u32 prev = x, next = intel_ring_wrap(ring, x + step); + int err = 0; + + err |= check_ring_direction(ring, next, next, 0); + err |= check_ring_direction(ring, prev, prev, 0); + err |= check_ring_direction(ring, next, prev, 1); + err |= check_ring_direction(ring, prev, next, -1); + + return err; +} + +static int check_ring_offset(struct intel_ring *ring, u32 x, u32 step) +{ + int err = 0; + + err |= check_ring_step(ring, x, step); + err |= check_ring_step(ring, intel_ring_wrap(ring, x + 1), step); + err |= check_ring_step(ring, intel_ring_wrap(ring, x - 1), step); + + return err; +} + +static int igt_ring_direction(void *dummy) +{ + struct intel_ring *ring; + unsigned int half = 2048; + int step, err = 0; + + ring = mock_ring(2 * half); + if (!ring) + return -ENOMEM; + + GEM_BUG_ON(ring->size != 2 * half); + + /* Precision of wrap detection is limited to ring->size / 2 */ + for (step = 1; step < half; step <<= 1) { + err |= check_ring_offset(ring, 0, step); + err |= check_ring_offset(ring, half, step); + } + err |= check_ring_step(ring, 0, half - 64); + + /* And check unwrapped handling for good measure */ + err |= check_ring_offset(ring, 0, 2 * half + 64); + err |= check_ring_offset(ring, 3 * half, 1); + + mock_ring_free(ring); + return err; +} + +int intel_ring_mock_selftests(void) +{ + static const struct i915_subtest tests[] = { + SUBTEST(igt_ring_direction), + }; + + return i915_subtests(tests, NULL); +} --- a/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h +++ b/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h @@ -20,6 +20,7 @@ selftest(fence, i915_sw_fence_mock_selft selftest(scatterlist, scatterlist_mock_selftests) selftest(syncmap, i915_syncmap_mock_selftests) selftest(uncore, intel_uncore_mock_selftests) +selftest(ring, intel_ring_mock_selftests) selftest(engine, intel_engine_cs_mock_selftests) selftest(timelines, intel_timeline_mock_selftests) selftest(requests, i915_request_mock_selftests)