Re: [PATCH] KVM: PPC: Book3S HV: Fix conversion to gfn-based MMU notifier callbacks

[Sean Christopherson <seanjc@google.com>]

On Wed, May 05, 2021, Nicholas Piggin wrote:
> Commit b1c5356e873c ("KVM: PPC: Convert to the gfn-based MMU notifier
> callbacks") causes unmap_gfn_range and age_gfn callbacks to only work
> on the first gfn in the range. It also makes the aging callbacks call
> into both radix and hash aging functions for radix guests. Fix this.

Ugh, the rest of kvm_handle_hva_range() was so similar to the x86 code that I
glossed right over the for-loop.  My apologies :-/

> Add warnings for the single-gfn calls that have been converted to range
> callbacks, in case they ever receieve ranges greater than 1.
> 
> Fixes: b1c5356e873c ("KVM: PPC: Convert to the gfn-based MMU notifier callbacks")
> Reported-by: Bharata B Rao <bharata@linux.ibm.com>
> Tested-by: Bharata B Rao <bharata@linux.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
> The e500 change in that commit also looks suspicious, why is it okay
> to remove kvm_flush_remote_tlbs() there? Also is the the change from
> returning false to true intended?

The common code interprets a return of "true" as "do kvm_flush_remote_tlbs()".
There is technically a functional change, as the deferring the flush to common
code will batch flushes if the invalidation spans multiple memslots.  But the
mmu_lock is held the entire time, so batching is a good thing unless e500 has
wildly different MMU semantics.