Re: [PATCH 3/3] arm, arm64: KVM: handle potential incoherency of readonly memslots

Jon Masters
2014-11-20T19:50:03Z

On 11/20/2014 01:40 PM, Peter Maydell wrote:
> On 20 November 2014 18:35, Mario Smarduch <m.smarduch@samsung.com> wrote:
>> I think beyond consistency, there should be no double mappings with
>> conflicting attributes at any time or CPU state is undefined.
>
> The situation is not so bleak as this. See section B2.9 "Mismatched
> memory attributes" in the ARMv8 ARM ARM (DDI0487A.d), which lays
> out in some detail what the results of mismatched attributes are
> (generally, you lose ordering or coherency guarantees you might
> have hoped to have). They're not pretty, but it's not as bad
> as completely UNPREDICTABLE behaviour.

Quick side note that I did raise exactly this issue with the ARM
Architecture team several years ago (that of missmatched memory
attributes between a guest and hypervisor) and it is a known concern.
I'm personally concerned about a couple of things that I won't go into
here but will followup on what the longer term plan might be.

Jon.