Peter Maydell <peter.mayd...@linaro.org> 于2018年9月13日周四 上午8:31写道：
> On 12 September 2018 at 18:43, Laszlo Ersek <ler...@redhat.com> wrote: > > On 09/12/18 14:54, Peter Maydell wrote: > >> There's patches on-list which drop the old_mmio field from the > MemoryRegion > >> struct entirely, so I think this patch as it stands is obsolete. > >> > >> Currently our semantics are "you must provide both read and write, even > >> if one of them just always returns 0 / does nothing / returns an error". > > > > That's new to me. Has this always been the case? > > Pretty sure it has, yes, because the code assumes that if you can > get a guest read then your MemoryRegion provides an accessor for it. > If your guest never actually tries to do a read then of course we'll > never notice... > > > There are several > > static MemoryRegionOps structures that don't conform. (See the end of my > > other email: > > < > 84da6f02-1f60-4bc7-92da-6a7f74deded3@redhat.com">http://mid.mail-archive.com/84da6f02-1f60-4bc7-92da-6a7f74deded3@redhat.com > >.) > > Beyond the one that Li Qiang reported directly ("fw_cfg_ctl_mem_read"). > > > > Are all of those ops guest-triggerable QEMU crashers? > > Some of them are special cases like the notdirty-memory one where > reads always go to host RAM rather than taking the slow path via > the io accessor. But others are probably guest crashers. > > >> We could probably reasonably assert this at the point when the > >> MemoryRegionOps is registered. > > > > Apparently, we should have... > > Yeah. Or we could define a default for if there's no read function, > which I guess should be the same as what we do if > memory_region_access_valid() fails. If we want that then the > simplest thing is for memory_region_access_valid() itself to > check that at least one of the accessor functions exists and > return false if none do. I thinks this proposal makes sense as every memory region write/read will go to this path and also the device code can make no change. Thanks, Li Qiang (But as I mention above we should get > all the "old_mmio is going away" patches in first and base the > change on that, or there'll be a conflict.) > > > thanks > -- PMM >
