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From:   Yu Zhao <yuzhao@google.com>
Date:   Thu, 8 Jun 2023 16:13:44 -0600
Message-ID: <CAOUHufbik3N9+K78=yGMZyERfD2o1o3kNgVoR73qKxWyQ2_3VQ@mail.gmail.com>
Subject: Re: [PATCH v1 1/3] KVM: arm64: Consistently use free_removed_table()
 for stage-2
To:     Chun-Tse Shao <ctshao@google.com>
Cc:     linux-kernel@vger.kernel.org, oliver.upton@linux.dev,
        Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Ben Gardon <bgardon@google.com>,
        Gavin Shan <gshan@redhat.com>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
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On Thu, Jun 8, 2023 at 4:06=E2=80=AFPM Chun-Tse Shao <ctshao@google.com> wr=
ote:
>
> From: Oliver Upton <oliver.upton@linux.dev>
>
> free_removed_table() is essential to the RCU-protected parallel walking
> scheme, as behind the scenes the cleanup is deferred until an RCU grace
> period. Nonetheless, the stage-2 unmap path calls put_page() directly,
> which leads to table memory being freed inline with the table walk.
>
> This is safe for the time being, as the stage-2 unmap walker is called
> while holding the write lock. A future change to KVM will further relax
> the locking mechanics around the stage-2 page tables to allow lock-free
> walkers protected only by RCU. As such, switch to the RCU-safe mechanism
> for freeing table memory.
>
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> Signed-off-by: Chun-Tse Shao <ctshao@google.com>

Acked-by: Yu Zhao <yuzhao@google.com>