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).