[PATCH] ARM64: KVM: Fix coherent_icache_guest_page() for host with external L3-cache.

Marc Zyngier marc.zyngier at arm.com
Wed Aug 14 11:49:24 EDT 2013

On 2013-08-14 16:35, Peter Maydell wrote:
> On 14 August 2013 16:23, Marc Zyngier <marc.zyngier at arm.com> wrote:
>> On 2013-08-14 15:22, Anup Patel wrote:
>>> It seems a bit unnatural to have cache cleaning is user-space. I am
>>> sure
>>> other architectures don't have such cache cleaning in user-space 
>>> for
>>> KVM.
>> Well, we have it on AArch64. Why would we blindly nuke the whole 
>> cache
>> if we can do the right thing, efficiently, on the right range?
> When exactly would userspace have to care about the cache?

Only for the initial payload, I'd expect. Unless I've missed something 
more crucial?

> This patch isn't exactly clear about the circumstances. I
> think you'd need a really strong reason for not dealing with
> this in the kernel -- in general userspace KVM tools don't
> otherwise have to deal with cache maintenance at all.

I believe we *could* do it in the kernel, just at the expense of a lot 
more CPU cycles.

A possible alternative would be to use HCR.DC, but I need to have a 
look and see what it breaks...

Fast, cheap, reliable. Pick two.

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