Re: [PATCH 4/4] arm/arm64: KVM: use kernel mapping to perform invalidation on page fault

[Christoffer Dall <christoffer.dall@linaro.org>]

On Sun, Jan 11, 2015 at 05:37:52PM +0000, Peter Maydell wrote:
> On 11 January 2015 at 12:33, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
> > On Fri, Jan 09, 2015 at 03:28:58PM +0000, Peter Maydell wrote:
> >> But implementations are allowed to hit in the cache even
> >> when the cache is disabled. In particular, setting the guest
> >
> > But how can it hit anything when the icache for the used VMID is
> > guaranteed to be clear (maybe that requires another full icache
> > invalidate for that VMID for PSCI reset)?
> 
> The point is that at the moment we don't do anything to
> guarantee that we've cleared the icache. 

that's not entirely accurate, I assume all of the icache is
invalidated/cleaned at system bring-up time, and every time we re-use a
VMID (when we start a VMID rollover) we invalidate the entire icache.

> (Plus could there be
> stale data in the icache for this physical CPU for this VMID
> because we've run some other vCPU on it? Or does the process
> of rescheduling vCPUs across pCPUs and guest ASID management
> deal with that?)

we don't clear the icache for vCPUs migrating onto other pCPUs but
invalidating the icache on a page fault won't guarantee that either.  Do
we really need to do that?

> 
> You probably want to clear the icache on vcpu (re-)init rather
> than reset, though (no guarantee that userspace is going to
> handle system resets via PSCI).
> 
Yes, good point.

-Christoffer