Re: [PATCH 3/3] docs/system/arm/virt: Fix documentation for the 'highmem' option

[Peter Maydell]

On Sun, 22 Aug 2021 at 15:45, Marc Zyngier <maz@kernel.org> wrote:
>
> The documentation for the 'highmem' option indicates that it controls
> the placement of both devices and RAM. The actual behaviour of QEMU
> seems to be that RAM is allowed to go beyond the 4GiB limit, and
> that only devices are constraint by this option.
>
> Align the documentation with the actual behaviour.

I think it would be better to align the behaviour with the documentation.

The intent of 'highmem' is to allow a configuration for use with guests
that can't address more than 32 bits (originally, 32-bit guests without
LPAE support compiled in). It seems like a bug that we allow the user
to specify more RAM than will fit into that 32-bit range. We should
instead make QEMU exit with an error if the user tries to specify
both highmem=off and a memory size that's too big to fit.

thanks
-- PMM