Re: [PATCH] mem/x86: add processor address space check for VM memory

[Ani Sinha <anisinha@redhat.com>]

On Mon, Sep 18, 2023 at 3:49 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 18.09.23 12:11, Ani Sinha wrote:
>
> >
> >     Ok hopefully my last question. I am still confused on something.
> >     Does the above mean that the hole64 will actually start from an
> >     address that is beyond maxram? Like basically if you added all of
> >     ram_below_4G, ram_above_4G, hot plug_mem and pci_hole64 then can it
> >     exceed maxram? I think it will. Does this not an issue?
>
> If you'd have a 2 GiB VM, the device memory region and hole64 would
> always be placed >= 4 GiB address, yes.
>
> As maxram is just a size, and not a PFN, I don't think there is any
> issue with that.

So this is all just a scheme to decide what to place where with maxram
amount of memory available. When the processor needs to access the
memory mapped PCI device, its simply dynamically mapped to the
available physical ram. Is my understanding correct here?

>
> ms->maxram_size is usually only used in combination with ms->ram_size to
> detect if memory devices will be enabled, and to size that region for
> memory devices.
>
> --
> Cheers,
>
> David / dhildenb
>