drm/i915/execlists: Track inflight CCID

The presumption is that by using a circular counter that is twice as
large as the maximum ELSP submission, we would never reuse the same CCID
for two inflight contexts.

However, if we continually preempt an active context such that it always
remains inflight, it can be resubmitted with an arbitrary number of
paired contexts. As each of its paired contexts will use a new CCID,
eventually it will wrap and submit two ELSP with the same CCID.

Rather than use a simple circular counter, switch over to a small bitmap
of inflight ids so we can avoid reusing one that is still potentially
active.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1796
Fixes: 2935ed5339c4 ("drm/i915: Remove logical HW ID")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200428184751.11257-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 470bdc73220a0cf45a164e8d995e58c515e5c0b3..cfe4feaee98274d3fda8738eb2e63c4de3c5e128 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -309,8 +309,7 @@ struct intel_engine_cs {
        u32 context_size;
        u32 mmio_base;
 
-       unsigned int context_tag;
-#define NUM_CONTEXT_TAG roundup_pow_of_two(2 * EXECLIST_MAX_PORTS)
+       unsigned long context_tag;
 
        struct rb_node uabi_node;
 

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 7d56207276d5ddc47387c2bc57eec759c6278555..05e2bb483db3a40c3f8be1850ef30877ea5761ac 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1389,13 +1389,17 @@ __execlists_schedule_in(struct i915_request *rq)
 
        if (ce->tag) {
                /* Use a fixed tag for OA and friends */
+               GEM_BUG_ON(ce->tag <= BITS_PER_LONG);
                ce->lrc.ccid = ce->tag;
        } else {
                /* We don't need a strict matching tag, just different values */
-               ce->lrc.ccid =
-                       (++engine->context_tag % NUM_CONTEXT_TAG) <<
-                       (GEN11_SW_CTX_ID_SHIFT - 32);
-               BUILD_BUG_ON(NUM_CONTEXT_TAG > GEN12_MAX_CONTEXT_HW_ID);
+               unsigned int tag = ffs(engine->context_tag);
+
+               GEM_BUG_ON(tag == 0 || tag >= BITS_PER_LONG);
+               clear_bit(tag - 1, &engine->context_tag);
+               ce->lrc.ccid = tag << (GEN11_SW_CTX_ID_SHIFT - 32);
+
+               BUILD_BUG_ON(BITS_PER_LONG > GEN12_MAX_CONTEXT_HW_ID);
        }
 
        ce->lrc.ccid |= engine->execlists.ccid;
@@ -1439,7 +1443,8 @@ static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
 
 static inline void
 __execlists_schedule_out(struct i915_request *rq,
-                        struct intel_engine_cs * const engine)
+                        struct intel_engine_cs * const engine,
+                        unsigned int ccid)
 {
        struct intel_context * const ce = rq->context;
 
@@ -1457,6 +1462,14 @@ __execlists_schedule_out(struct i915_request *rq,
            i915_request_completed(rq))
                intel_engine_add_retire(engine, ce->timeline);
 
+       ccid >>= GEN11_SW_CTX_ID_SHIFT - 32;
+       ccid &= GEN12_MAX_CONTEXT_HW_ID;
+       if (ccid < BITS_PER_LONG) {
+               GEM_BUG_ON(ccid == 0);
+               GEM_BUG_ON(test_bit(ccid - 1, &engine->context_tag));
+               set_bit(ccid - 1, &engine->context_tag);
+       }
+
        intel_context_update_runtime(ce);
        intel_engine_context_out(engine);
        execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
@@ -1482,15 +1495,17 @@ execlists_schedule_out(struct i915_request *rq)
 {
        struct intel_context * const ce = rq->context;
        struct intel_engine_cs *cur, *old;
+       u32 ccid;
 
        trace_i915_request_out(rq);
 
+       ccid = rq->context->lrc.ccid;
        old = READ_ONCE(ce->inflight);
        do
                cur = ptr_unmask_bits(old, 2) ? ptr_dec(old) : NULL;
        while (!try_cmpxchg(&ce->inflight, &old, cur));
        if (!cur)
-               __execlists_schedule_out(rq, old);
+               __execlists_schedule_out(rq, old, ccid);
 
        i915_request_put(rq);
 }
@@ -3990,7 +4005,7 @@ static void enable_execlists(struct intel_engine_cs *engine)
 
        enable_error_interrupt(engine);
 
-       engine->context_tag = 0;
+       engine->context_tag = GENMASK(BITS_PER_LONG - 2, 0);
 }
 
 static bool unexpected_starting_state(struct intel_engine_cs *engine)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 04ad219606886ca6886d0e97e5c3631f53835f94..c533f569dd42cf83c02745833954ee24ec26ce75 100644 (file)
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -1280,11 +1280,10 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
                        ((1U << GEN11_SW_CTX_ID_WIDTH) - 1) << (GEN11_SW_CTX_ID_SHIFT - 32);
                /*
                 * Pick an unused context id
-                * 0 - (NUM_CONTEXT_TAG - 1) are used by other contexts
+                * 0 - BITS_PER_LONG are used by other contexts
                 * GEN12_MAX_CONTEXT_HW_ID (0x7ff) is used by idle context
                 */
                stream->specific_ctx_id = (GEN12_MAX_CONTEXT_HW_ID - 1) << (GEN11_SW_CTX_ID_SHIFT - 32);
-               BUILD_BUG_ON((GEN12_MAX_CONTEXT_HW_ID - 1) < NUM_CONTEXT_TAG);
                break;
        }
 

diff --git a/drivers/gpu/drm/i915/selftests/i915_vma.c b/drivers/gpu/drm/i915/selftests/i915_vma.c
index 58b5f40a07dd6be16eedab36d8c52d9ff9e2e914..af89c7fc8f59340bad9d38628b0c6f751caed521 100644 (file)
--- a/drivers/gpu/drm/i915/selftests/i915_vma.c
+++ b/drivers/gpu/drm/i915/selftests/i915_vma.c
@@ -173,7 +173,7 @@ static int igt_vma_create(void *arg)
                }
 
                nc = 0;
-               for_each_prime_number(num_ctx, 2 * NUM_CONTEXT_TAG) {
+               for_each_prime_number(num_ctx, 2 * BITS_PER_LONG) {
                        for (; nc < num_ctx; nc++) {
                                ctx = mock_context(i915, "mock");
                                if (!ctx)