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Date:   Fri, 6 Dec 2019 11:57:42 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Ben Gardon <bgardon@google.com>
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Peter Feiner <pfeiner@google.com>,
        Peter Shier <pshier@google.com>,
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        Jim Mattson <jmattson@google.com>
Subject: Re: [RFC PATCH 00/28] kvm: mmu: Rework the x86 TDP direct mapped case
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On Fri, Dec 06, 2019 at 11:55:42AM -0800, Ben Gardon wrote:
> I'm finally back in the office. Sorry for not getting back to you sooner.
> I don't think it would be easy to send the synchronization changes
> first. The reason they seem so small is that they're all handled by
> the iterator. If we tried to put the synchronization changes in
> without the iterator we'd have to 1.) deal with struct kvm_mmu_pages,
> 2.) deal with the rmap, and 3.) change a huge amount of code to insert
> the synchronization changes into the existing framework. The changes
> wouldn't be mechanical or easy to insert either since a lot of
> bookkeeping is currently done before PTEs are updated, with no
> facility for rolling back the bookkeeping on PTE cmpxchg failure. We
> could start with the iterator changes and then do the synchronization
> changes, but the other way around would be very difficult.

By synchronization changes, I meant switching to a r/w lock instead of a
straight spinlock.  Is that doable in a smallish series?