535.98

kernel-open/nvidia-uvm/uvm_migrate.c

@@ -134,6 +134,22 @@ static NV_STATUS block_migrate_map_unmapped_pages(uvm_va_block_t *va_block,
     // first map operation
     uvm_page_mask_complement(&va_block_context->caller_page_mask, &va_block->maybe_mapped_pages);
 
+    if (uvm_va_block_is_hmm(va_block) && !UVM_ID_IS_CPU(dest_id)) {
+        // Do not map pages that are already resident on the CPU. This is in
+        // order to avoid breaking system-wide atomic operations on HMM. HMM's
+        // implementation of system-side atomic operations involves restricting
+        // mappings to one processor (CPU or a GPU) at a time. If we were to
+        // grant a GPU a mapping to system memory, this gets into trouble
+        // because, on the CPU side, Linux can silently upgrade PTE permissions
+        // (move from read-only, to read-write, without any MMU notifiers
+        // firing), thus breaking the model by allowing simultaneous read-write
+        // access from two separate processors. To avoid that, just don't map
+        // such pages at all, when migrating.
+        uvm_page_mask_andnot(&va_block_context->caller_page_mask,
+                             &va_block_context->caller_page_mask,
+                             uvm_va_block_resident_mask_get(va_block, UVM_ID_CPU));
+    }
+
     // Only map those pages that are not mapped anywhere else (likely due
     // to a first touch or a migration). We pass
     // UvmEventMapRemoteCauseInvalid since the destination processor of a