On 08/04/2017 10:20 AM, Peter Maydell wrote: > 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. > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > --- > include/qom/cpu.h | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+)
Reviewed-by: Richard Henderson <richard.hender...@linaro.org> r~
