Re: [PATCH v2 1/5] hw/arm/virt: Key enablement of highmem PCIe on highmem_ecam

[Marc Zyngier <maz@kernel.org>]

Hi Eric,

On Wed, 05 Jan 2022 09:41:19 +0000,
Eric Auger <eric.auger@redhat.com> wrote:
> 
> couldn't you simply introduce highmem_redist which is truly missing. You
> could set it in virt_set_memmap() in case you skip extended_map overlay
> and use it in virt_gicv3_redist_region_count() as you did?
> In addition to the device memory top address check against the 4GB limit
> if !highmem, we should be fine then?

No, highmem really isn't nearly enough.

Imagine you have (like I do) a system with 36 bits of IPA space.
Create a VM with 8GB of RAM (which means the low-end of IPA space is
already 9GB). Obviously, highmem=true here. With the current code, we
will try to expose this PCI MMIO range, which falls way out of the IPA
space (you need at least 40 bits of IPA to even cover it with the
smallest configuration).

highmem really is a control that says 'things may live above 4GB'. It
doesn't say *how far* above 4GB it can be placed. Which is what I am
trying to address.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.