drm/i915/gt: Clear SET_PREDICATE_RESULT prior to executing the ring

Userspace may leave predication enabled upon return from the batch
buffer, which has the consequent of preventing all operation from the
ring from being executed, including all the synchronisation, coherency
control, arbitration and user signaling. This is more than just a local
gpu hang in one client, as the user has the ability to prevent the
kernel from applying critical workarounds and can cause a full GT reset.

We could simply execute MI_SET_PREDICATE upon return from the user
batch, but this has the repercussion of modifying the user's context
state. Instead, we opt to execute a fixup batch which by mixing
predicated operations can determine the state of the
SET_PREDICATE_RESULT register and restore it prior to the next userspace
batch. This allows us to protect the kernel's ring without changing the
uABI.

Suggested-by: Zbigniew Kempczynski <zbigniew.kempczynski@intel.com>
Signed-off-by: Chris Wilson <chris.p.wilson@intel.com>
Cc: Zbigniew Kempczynski <zbigniew.kempczynski@intel.com>
Cc: Thomas Hellstrom <thomas.hellstrom@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220425152317.4275-4-ramalingam.c@intel.com

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.h b/drivers/gpu/drm/i915/gt/intel_lrc.h
index 7371bb5c8129..31be734010db 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.h
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.h
@@ -145,4 +145,9 @@ static inline void lrc_runtime_stop(struct intel_context *ce)
 	WRITE_ONCE(stats->active, 0);
 }
 
+#define DG2_PREDICATE_RESULT_WA (PAGE_SIZE - sizeof(u64))
+#define DG2_PREDICATE_RESULT_BB (2048)
+
+u32 lrc_indirect_bb(const struct intel_context *ce);
+
 #endif /* __INTEL_LRC_H__ */