Re: [Qemu-devel] [PATCH v3] hw/arm/virt: Add high MMIO PCI region

[Pavel Fedin <p.fedin@samsung.com>]

 Hello!

> It matters because you can run 32 bit guests in 64-bit-capable
> CPUs.

 Yes, i know.

> I don't really want to have two different address layouts
> just to work around a kernel bug

 They will not be really different. Just for 32-bit machines there will be no second MMIO window, and for 64-bit ones there will be. Nothing else will be different.

> if we could fix the kernel bug instead...

 We could. But what about existing installations? They will be forced to upgrade kernels, we will not have backwards compatibility option. And users will complain that "my old VM stopped working with new qemu".
 Well, this discussion seems to be stuck, so let's move on. What is your final word? Options are:
1. Include second region unconditionally. Old 32-bit guests will stop working.
2. Add machine option to specify second region size. For 64-bits it will default to something, for 32-bits it will default to 0 (= off). It will be possible to turn on the region for 32-bit machines explicitly.
3. Include second region only on 64-bit guests. 32-bit ones will wait until somebody needs it.

 Your choice ?

 P.S. My 3.19 guest has LPAE disabled in the configuration. Perhaps my fault, but still it's a potential problem.
 

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia