From: Chris Wilson chris@chris-wilson.co.uk
commit dea8d5ce46d7e7f7270b9804df7d1174f88bfd99 upstream.
To enable non-persistent contexts, we require a means of cancelling any inflight work from that context. This is first done "gracefully" by using preemption to kick the active context off the engine, and then forcefully by resetting the engine if it is active. If we are unable to reset the engine to remove hostile userspace, we should not allow userspace to opt into using non-persistent contexts.
If the per-engine reset fails, we still do a full GPU reset, but that is rare and usually indicative of much deeper issues. The damage is already done. However, the goal of the interface to allow long running compute jobs without causing collateral damage elsewhere, and if we are unable to support that we should make that known by not providing the interface (and falsely pretending we can).
Fixes: a0e047156cde ("drm/i915/gem: Make context persistence optional") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Jon Bloomfield jon.bloomfield@intel.com Reviewed-by: Joonas Lahtinen joonas.lahtinen@linux.intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200130164553.1937718-1-chris... (cherry picked from commit d1b9b5f127bc3797fc274cfa4f363e039f045c3a) Signed-off-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/gem/i915_gem_context.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -484,6 +484,22 @@ static int __context_set_persistence(str if (!(ctx->i915->caps.scheduler & I915_SCHEDULER_CAP_PREEMPTION)) return -ENODEV;
+ /* + * If the cancel fails, we then need to reset, cleanly! + * + * If the per-engine reset fails, all hope is lost! We resort + * to a full GPU reset in that unlikely case, but realistically + * if the engine could not reset, the full reset does not fare + * much better. The damage has been done. + * + * However, if we cannot reset an engine by itself, we cannot + * cleanup a hanging persistent context without causing + * colateral damage, and we should not pretend we can by + * exposing the interface. + */ + if (!intel_has_reset_engine(&ctx->i915->gt)) + return -ENODEV; + i915_gem_context_clear_persistence(ctx); }