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

[Eric Auger <eric.auger@redhat.com>]

Hi Marc,

On 1/6/22 8:34 PM, Marc Zyngier wrote:
> 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).
In that case the he High MMIO region is accounted in the vms->highest_gpa:

    for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
        hwaddr size = extended_memmap[i].size;

        base = ROUND_UP(base, size);
        vms->memmap[i].base = base;
        vms->memmap[i].size = size;
        base += size;
    }
    vms->highest_gpa = base - 1;

and virt_kvm_type() should exit in that case at:
if (requested_pa_size > max_vm_pa_size) {
        error_report("-m and ,maxmem option values "
                     "require an IPA range (%d bits) larger than "
                     "the one supported by the host (%d bits)",
                     requested_pa_size, max_vm_pa_size);
        exit(1);
    }

?
>
> 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.

OK I will look at your v4 ;-)

Thanks

Eric
>
> Thanks,
>
> 	M.
>

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