The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 110f9efa858f584c6bed177cd48d0c0f526940e1 Mon Sep 17 00:00:00 2001
From: Chris Wilson chris@chris-wilson.co.uk Date: Mon, 13 Jul 2020 17:05:49 +0100 Subject: [PATCH] drm/i915/gt: Only swap to a random sibling once upon creation
The danger in switching at random upon intel_context_pin is that the context may still actually be inflight, as it will not be scheduled out until a context switch after it is complete -- that may be a long time after we do a final intel_context_unpin.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2118 Fixes: 6d06779e8672 ("drm/i915: Load balancing across a virtual engine") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: stable@vger.kernel.org # v5.3+ Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200713160549.17344-1-chris@c... (cherry picked from commit 90a987205c6cf74116a102ed446d22d92cdaf915) Signed-off-by: Jani Nikula jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index d270d2db6f0a..cb07e1d2a353 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -5396,13 +5396,8 @@ static void virtual_engine_initial_hint(struct virtual_engine *ve) * typically be the first we inspect for submission. */ swp = prandom_u32_max(ve->num_siblings); - if (!swp) - return; - - swap(ve->siblings[swp], ve->siblings[0]); - if (!intel_engine_has_relative_mmio(ve->siblings[0])) - virtual_update_register_offsets(ve->context.lrc_reg_state, - ve->siblings[0]); + if (swp) + swap(ve->siblings[swp], ve->siblings[0]); }
static int virtual_context_alloc(struct intel_context *ce) @@ -5415,15 +5410,9 @@ static int virtual_context_alloc(struct intel_context *ce) static int virtual_context_pin(struct intel_context *ce) { struct virtual_engine *ve = container_of(ce, typeof(*ve), context); - int err;
/* Note: we must use a real engine class for setting up reg state */ - err = __execlists_context_pin(ce, ve->siblings[0]); - if (err) - return err; - - virtual_engine_initial_hint(ve); - return 0; + return __execlists_context_pin(ce, ve->siblings[0]); }
static void virtual_context_enter(struct intel_context *ce) @@ -5770,6 +5759,7 @@ intel_execlists_create_virtual(struct intel_engine_cs **siblings,
ve->base.flags |= I915_ENGINE_IS_VIRTUAL;
+ virtual_engine_initial_hint(ve); return &ve->context;
err_put: