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

[Alexander Graf <agraf@csgraf.de>]

On 03.01.23 18:41, Peter Maydell wrote:
> 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).


Follow-up on this: Microsoft has fixed the issue in Windows. That won't 
make older versions work, but the current should be fine with GICv3:

https://fosstodon.org/@itanium/109909281184181276


Alex