On 09/05/2013 07:27 PM, Alexander Graf wrote: > > On 05.09.2013, at 09:40, Alexey Kardashevskiy wrote: > >> On 09/05/2013 05:08 PM, Alexander Graf wrote: >>> >>> >>> Am 05.09.2013 um 07:58 schrieb Alexey Kardashevskiy <a...@ozlabs.ru>: >>> >>>> On the real hardware, RTAS is called in real mode and therefore >>>> ignores top 4 bits of the address passed in the call. >>> >>> Shouldn't we ignore the upper 4 bits for every memory access in real mode, >>> not just that one parameter? >> >> We probably should but I just do not see any easy way of doing this. Yet >> another "Ignore N bits on the top" memory region type? No idea. > > Well, it already works for code that runs inside of guest context, because > there the softmmu code for real mode strips the upper 4 bits. > > I basically see 2 ways of fixing this "correctly": >
> 1) Don't access memory through cpu_physical_memory_rw or ldx_phys but > instead through real mode wrappers that strip the upper 4 bits, similar > to how we handle virtual memory differently from physical memory But there is no a ready wrapper for this, correct? I could not find any. I would rather do this, looks nicer than 2). > 2) Create 15 aliases to system_memory at the upper 4 bits of address > space. That should at the end of the day give you the same effect Wow. Is not that too much? Ooor since I am normally making bad decisions, I should do this :) > The fix as you're proposing it wouldn't work for indirect memory > descriptors. Imagine you have an "address" parameter that gives you a > pointer to a struct in memory that again contains a pointer. You still > want that pointer be interpreted correctly, no? Yes I do. I just think that having non zero bits at the top is a bug and I would not want the guest to continue sending bad addresses to the host. Or at least I want to know if it still happening. Now we know that the only occasion of this misbehaviour is the "stop-self" call and others works just fine. If something new comes up (what is pretty unlikely, otherwise we would have noticed this issue a loong time ago AND Paul already made&posted a patch for the host to fix __pa() so it is not going to happen on new kernels either), ok, we will think of fixing this. Doing in QEMU what the hardware does is a good thing but here I would think twice. -- Alexey