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

From: Pavel Fedin
Subject: Re: [Qemu-devel] [PATCH v3] hw/arm/virt: Add high MMIO PCI region
Date: Wed, 29 Jul 2015 13:03:57 +0300


> >  I'm not sure that ARM architecture has this machine_done callback.
> Maybe this would help you,
>    git grep machine_done

 Heh, i was not patient enough. I have already discovered this by myself, and 
yes, "virt" uses the
same mechanism. But, still, i perhaps can have problems with testing it.

> >  So, can we leave fixed layout for now?
> I suppose we could, it just means that we will have to add version-ed 
> machines like
> it's done on x86 to keep memory layout on old machine type the same so that
> hardware won't change under guest's feet unexpectedly.

 First, "virt" is completely virtual hardware. It does not exist in real world.
 Second, ARM architecture is flexible by definition. Guest is never expected to 
use hardcoded
addresses, it is expected to read device tree. And, if base address of RAM 
changes, or base address
of PCI region changes, nothing bad should happen.

> Also in light of guests with huge memory size, 512Gb  gap for RAM seems too 
> small,
> what are limitations of ARM64 regarding max supported physical address bits?

 40 bits IIRC.

> Could we put this 64 bit PCI hole at the end of address space, leaving the 
> rest of
> address space for RAM or whatever?

 I've done exactly this. Start = 512GB and size = 512GB. 
0x8000000000...0xFFFFFFFFFF. I've done this
after Paolo's comment that 2G is still small. And i agree because single 
ivshmem could be used by
lots of VMs.

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

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