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c44d323359
Currently we have a rather half-baked setup for allowing CPUs to generate exceptions on accesses to invalid memory: the CPU has a cpu_unassigned_access() hook which the memory system calls in unassigned_mem_write() and unassigned_mem_read() if the current_cpu pointer is non-NULL. This was originally designed before we implemented the MemTxResult type that allows memory operations to report a success or failure code, which is why the hook is called right at the bottom of the memory system. The major problem with this is that it means that the hook can be called even when the access was not actually done by the CPU: for instance if the CPU writes to a DMA engine register which causes the DMA engine to begin a transaction which has been set up by the guest to operate on invalid memory then this will casue the CPU to take an exception incorrectly. Another minor problem is that currently if a device returns a transaction error then this won't turn into a CPU exception at all. The right way to do this is to have allow the CPU to respond to memory system transaction failures at the point where the CPU specific code calls into the memory system. Define a new QOM CPU method and utility function cpu_transaction_failed() which is called in these cases. The functionality here overlaps with the existing cpu_unassigned_access() because individual target CPUs will need some work to convert them to the new system. When this transition is complete we can remove the old cpu_unassigned_access() code. Backports commit 0dff0939f6fc6a7abd966d4295f06a06d7a01df9 from qemu |
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