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From:   Oliver Upton <oliver.upton@linux.dev>
To:     Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, Reiji Watanabe <reijiw@google.com>,
        Ricardo Koller <ricarkol@google.com>,
        David Matlack <dmatlack@google.com>,
        Quentin Perret <qperret@google.com>,
        Ben Gardon <bgardon@google.com>, Gavin Shan <gshan@redhat.com>,
        Peter Xu <peterx@redhat.com>, Will Deacon <will@kernel.org>,
        Sean Christopherson <seanjc@google.com>, kvmarm@lists.linux.dev
Subject: Re: [PATCH v3 00/15] KVM: arm64: Parallel stage-2 fault handling
Message-ID: <Y1sWnyHvMWP/DhHm@google.com>
References: <20221027221752.1683510-1-oliver.upton@linux.dev>
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On Thu, Oct 27, 2022 at 10:17:37PM +0000, Oliver Upton wrote:
> Presently KVM only takes a read lock for stage 2 faults if it believes
> the fault can be fixed by relaxing permissions on a PTE (write unprotect
> for dirty logging). Otherwise, stage 2 faults grab the write lock, which
> predictably can pile up all the vCPUs in a sufficiently large VM.
> 
> Like the TDP MMU for x86, this series loosens the locking around
> manipulations of the stage 2 page tables to allow parallel faults. RCU
> and atomics are exploited to safely build/destroy the stage 2 page
> tables in light of multiple software observers.
> 
> Patches 1-4 clean up the context associated with a page table walk / PTE
> visit. This is helpful for:
>  - Extending the context passed through for a visit
>  - Building page table walkers that operate outside of a kvm_pgtable
>    context (e.g. RCU callback)

As is always the case, I failed to update the changelogs when twiddling
things around a bit more.

Specifically, 8/15 and 14/15 don't directly match the diffs anymore. I
wont respin (yet) to avoid bombarding mailboxes.

--
Thanks,
Oliver