On Mon, Apr 19, 2021 at 10:58 PM Philippe Mathieu-Daudé <f4...@amsat.org> wrote: > On 4/19/21 10:13 PM, Mark Cave-Ayland wrote: > > On 17/04/2021 15:02, Philippe Mathieu-Daudé wrote: > > > >> Since commit 2cdfcf272d ("memory: assign MemoryRegionOps to all > >> regions"), all newly created regions are assigned with > >> unassigned_mem_ops (which might be then overwritten). > >> > >> When using aliased container regions, and there is no region mapped > >> at address 0 in the container, the memory_region_dispatch_read() > >> and memory_region_dispatch_write() calls incorrectly return the > >> container unassigned_mem_ops, because the alias offset is not used. > >> > >> The memory_region_init_alias() flow is: > >> > >> memory_region_init_alias() > >> -> memory_region_init() > >> -> object_initialize(TYPE_MEMORY_REGION) > >> -> memory_region_initfn() > >> -> mr->ops = &unassigned_mem_ops; > >> > >> Later when accessing the alias, the memory_region_dispatch_read() > >> flow is: > >> > >> memory_region_dispatch_read(offset) > >> -> memory_region_access_valid(mr) <- offset is ignored > >> -> mr->ops->valid.accepts() > >> -> unassigned_mem_accepts() > >> <- false > >> <- false > >> <- MEMTX_DECODE_ERROR > >> > >> The caller gets a MEMTX_DECODE_ERROR while the access is OK. > >> > >> Fix by dispatching aliases recusirvely, accessing its origin region > >> after adding the alias offset. > >> > >> Signed-off-by: Philippe Mathieu-Daudé <f4...@amsat.org> > >> --- > >> v3: > >> - reworded, mentioning the "alias to container" case > >> - use recursive call instead of while(), because easier when debugging > >> therefore reset Richard R-b tag. > >> v2: > >> - use while() > >> --- > >> softmmu/memory.c | 10 ++++++++++ > >> 1 file changed, 10 insertions(+) > >> > >> diff --git a/softmmu/memory.c b/softmmu/memory.c > >> index d4493ef9e43..23bdbfac079 100644 > >> --- a/softmmu/memory.c > >> +++ b/softmmu/memory.c > >> @@ -1442,6 +1442,11 @@ MemTxResult > >> memory_region_dispatch_read(MemoryRegion *mr, > >> unsigned size = memop_size(op); > >> MemTxResult r; > >> + if (mr->alias) { > >> + return memory_region_dispatch_read(mr->alias, > >> + addr + mr->alias_offset, > >> + pval, op, attrs); > >> + } > >> if (!memory_region_access_valid(mr, addr, size, false, attrs)) { > >> *pval = unassigned_mem_read(mr, addr, size); > >> return MEMTX_DECODE_ERROR; > >> @@ -1486,6 +1491,11 @@ MemTxResult > >> memory_region_dispatch_write(MemoryRegion *mr, > >> { > >> unsigned size = memop_size(op); > >> + if (mr->alias) { > >> + return memory_region_dispatch_write(mr->alias, > >> + addr + mr->alias_offset, > >> + data, op, attrs); > >> + } > >> if (!memory_region_access_valid(mr, addr, size, true, attrs)) { > >> unassigned_mem_write(mr, addr, data, size); > >> return MEMTX_DECODE_ERROR; > > > > Whilst working on my q800 patches I realised that this was a similar > > problem to the one I had with my macio.alias implementation at [1]: > > except that in my case the unassigned_mem_ops mr->ops->valid.accepts() > > function was being invoked on a ROM memory region instead of an alias. I > > think this is exactly the same issue that you are attempting to fix with > > your related patch at > > https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg03190.html > > ("memory: Initialize MemoryRegionOps for RAM memory regions"). > > So if 2 contributors hit similar issues, there is something wrong with > the API. I don't see your use case or mine as forbidded by the > documentation in "exec/memory.h". > > My patch might not be the proper fix, but we need to figure out how > to avoid others to hit the same problem, as it is very hard to debug. > > At least an assertion and a comment.
Something like: -- >8 -- diff --git a/softmmu/memory.c b/softmmu/memory.c index d4493ef9e43..e031ac6e074 100644 --- a/softmmu/memory.c +++ b/softmmu/memory.c @@ -1442,6 +1442,7 @@ MemTxResult memory_region_dispatch_read(MemoryRegion *mr, unsigned size = memop_size(op); MemTxResult r; + assert(!(mr->alias && !mr>alias_offset)); /* Use AddressSpace API instead */ if (!memory_region_access_valid(mr, addr, size, false, attrs)) { *pval = unassigned_mem_read(mr, addr, size); return MEMTX_DECODE_ERROR; --- > > I eventually realised that I needed functions that could dispatch > > reads/writes to both IO memory regions and ROM memory regions, and that > > functionality is covered by the address_space_*() access functions. > > Using the address_space_*() functions I was then able to come up with > > the working implementation at [2] that handles accesses to both IO > > memory regions and ROM memory regions correctly. > > > > The reason I initially used the > > memory_region_dispatch_read()/memory_region_dispatch_write() functions > > was because I could see that was how the virtio devices dispatched > > accesses through the proxy. However I'm wondering now if this API can > > only be used for terminating IO memory regions, and so the alias_offset > > that you're applying above should actually be applied elsewhere instead. > > I figured out the AddressSpace API make these cases simpler, but IIRC > there is some overhead, some function tries to resolve / update > something and iterate over a list. While from the MemoryRegion API we > already know which region we want to access. > > I Cc'ed Peter considering him expert in this area, but don't know else > who to ask for help on this topic... > > > ATB, > > > > Mark. > > > > [1] > > https://github.com/mcayland/qemu/commit/56f8639fbecb8a8e323ce486e20cbe309e807419 > > > > > > [2] > > https://github.com/mcayland/qemu/commit/c1fa32da188bb2ce23faf1728228c1714672270d > > > >