Re: [PATCH 0/2] hw/intc/arm_gicv3: Bump ITT entry size to 16

[Peter Maydell]

On Fri, 23 Dec 2022 at 08:50, Alexander Graf <agraf@csgraf.de> wrote:
>
> While trying to make Windows work with GICv3 emulation, I stumbled over
> the fact that it only supports ITT entry sizes that are power of 2 sized.
>
> While the spec allows arbitrary sizes, in practice hardware will always
> expose power of 2 sizes and so this limitation is not really a problem
> in real world scenarios. However, we only expose a 12 byte ITT entry size
> which makes Windows blue screen on boot.
>
> The easy way to get around that problem is to bump the size to 16. That
> is a power of 2, basically is what hardware would expose given the amount
> of bits we need per entry and doesn't break any existing scenarios. To
> play it safe, this patch set only bumps them on newer machine types.

This is a Windows bug and should IMHO be fixed in that guest OS.
Changing the ITT entry size of QEMU's implementation introduces
an unnecessary incompatibility in migration and wastes memory
(we're already a bit unnecessarily profligate with ITT entries
compared to real hardware).

thanks
-- PMM