vishals4gh
commented
3 years ago Rather than a merge request, this is more of review request to seek more feedback about whether: 1) This issue is something that should be addressed 2) The approach I tried to pursue is fine to proceed with This patch is still WIP.
Thanks, Vishal
By default most of the platforms map all the DRAM at boot time causing scenarios where same physical address initially mapped with cacheable attributes maybe allowed to get mapped with non-cacheable attributes via different VM range. This is discouraged in architectures like ARM and gets tedious to ensure the coherent view of DRAM with other masters.
This change ensures following for qemu-arm platform: 1) Add support of Arenas which might not be mapped in kernel space initially after platform is setup. 2) All the malloc calls use the pages from the arenas which are already mapped to kernel space. 3) vmm_alloc APIs use the arenas which are not already mapped to any virtual address range. 4) vmm_free_region for memory allocated via vmm_alloc APIS using cacheable memory mappings will clean caches for reuse by the next vmm_alloc* API call that can map memory with different attributes. 5) Memory for unmapped arena is initially allowed to be mapped and then unmapped later during platform initialization.
This avoids remapping of the same physical memory to different virtual address ranges with different memory attributes. This effectively ensures that at any given memory from the vmm_arena can be owned by singal entity with a particular memory attributes.
Caveats: 1) paddr_to_kvaddr API will not work for Physical addresses allocated using vmm_alloc* APIs
ToDo: 1) Address the shortfalls of the current implementation 2) Update other platforms to allow unmapped ram arenas if this implementation is ok to pursue.
Signed-off-by: vannapurve vannapurve@google.com