On 4 July 2018 at 16:51, Will Deacon <will.deacon@xxxxxxx> wrote: > On Wed, Jul 04, 2018 at 03:41:18PM +0100, Marc Zyngier wrote: >> Not really. Let's say I want my IPA space split in two: memory covers >> the low 47 bit, and I want MMIO spanning the top 47 bit. With your >> scheme, you'd end-up with a 47bit IPA space, while you really want 48 >> bits (MMIO space implemented by userspace isn't registered to the >> kernel). > > That still sounds quite niche for a VM. Does QEMU do that? Not at 47 bits, but we have RAM up to the 256GB mark, and MMIO above that (including a large PCI window), so the general arrangement of having the top end of the IPA space not necessarily be things we've told the kernel about definitely exists. thanks -- PMM
