Re: [RFC PATCH 3/3] KVM: x86/mmu: skip zap maybe-dma-pinned pages for NUMA migration

[Yan Zhao]

On Tue, Aug 08, 2023 at 11:32:37AM -0300, Jason Gunthorpe wrote:
.... 
> > This really needs to be fixed in the primary MMU and not require any direct
> > involvement from secondary MMUs, e.g. the mmu_notifier invalidation itself needs
> > to be skipped.
> 
> This likely has the same issue you just described, we don't know if it
> can be skipped until we iterate over the PTEs and by then it is too
> late to invoke the notifier. Maybe some kind of abort and restart
The problem is that KVM currently performs the zap in handler of .invalidate_range_start(),
so before abort in mm, KVM has done the zap in secondary MMU.

Or, could we move the zap in KVM side to handler of .invalidate_range_end() only for
MMU_NOTIFY_PROTECTION_VMA and MMU_NOTIFIER_RANGE_NUMA?

Then, in mm side, we could do the abort and update the range to contain only successful
subrange .invalidate_range_end().

Is that acceptable?

> scheme could work?
>