linux-kernel - Re: [PATCH v1 1/3] KVM: arm64: Consistently use free_removed

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Message-ID: <CAOUHufbik3N9+K78=yGMZyERfD2o1o3kNgVoR73qKxWyQ2_3VQ@mail.gmail.com>
Date:   Thu, 8 Jun 2023 16:13:44 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Chun-Tse Shao <ctshao@...gle.com>
Cc:     linux-kernel@...r.kernel.org, oliver.upton@...ux.dev,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ben Gardon <bgardon@...gle.com>,
        Gavin Shan <gshan@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v1 1/3] KVM: arm64: Consistently use free_removed_table()
 for stage-2

On Thu, Jun 8, 2023 at 4:06 PM Chun-Tse Shao <ctshao@...gle.com> wrote:
>
> From: Oliver Upton <oliver.upton@...ux.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@...ux.dev>
> Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>

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