On 17/12/19 19:17, Peter Maydell wrote: > On Tue, 17 Dec 2019 at 16:57, Richard Henderson > <richard.hender...@linaro.org> wrote: >> >> On 12/17/19 1:58 AM, Christophe de Dinechin wrote: >>> >>> >>>> On 17 Dec 2019, at 11:51, Paolo Bonzini <pbonz...@redhat.com> wrote: >>>> Yes, the idea is that you could have for one version of the device >>>> >>>> parent 0x000-0x7ff >>>> stuff 0x000-0x3ff >>>> morestuff 0x400-0x7ff >>>> >>>> and for another >>>> >>>> parent 0x000-0x3ff >>>> stuff 0x000-0x3ff >>>> morestuff 0x400-0x7ff >>>> >>>> where parent is the BAR, and you can share the code to generate the tree >>>> underneath parent. >>> >>> I can see why you would have code reuse reasons to do that, >>> but frankly it looks buggy and confusing. In the rare cases >>> where this is indented, maybe add a flag making it explicit? >> >> The guest OS is programming the BAR, producing a configuration that, while it >> doesn't make sense, is also legal per PCI. QEMU cannot abort for this >> configuration. > > Does guest programming of the PCI BAR size actually change the size > of the 'parent' region, or does it just result in the creation > of an appropriately sized alias into 'parent' ?
Resizable BARs are not handled by the PCI host bridge but rather from the device itself, so the device is free to handle them either way. Paolo
