From: Marc Zyngier <maz@kernel.org>
To: Quentin Perret <qperret@google.com>
Cc: will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com,
catalin.marinas@arm.com, suzuki.poulose@arm.com,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kernel-team@android.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/7] KVM: arm64: Move hyp_pool locking out of refcount helpers
Date: Tue, 01 Jun 2021 13:02:00 +0100 [thread overview]
Message-ID: <87sg2123pj.wl-maz@kernel.org> (raw)
In-Reply-To: <20210527125134.2116404-2-qperret@google.com>
On Thu, 27 May 2021 13:51:28 +0100,
Quentin Perret <qperret@google.com> wrote:
>
> The hyp_page refcount helpers currently rely on the hyp_pool lock for
> serialization. However, this means the refcounts can't be changed from
> the buddy allocator core as it already holds the lock, which means pages
> have to go through odd transient states.
>
> For example, when a page is freed, its refcount is set to 0, and the
> lock is transiently released before the page can be attached to a free
> list in the buddy tree. This is currently harmless as the allocator
> checks the list node of each page to see if it is available for
> allocation or not, but it means the page refcount can't be trusted to
> represent the state of the page even if the pool lock is held.
>
> In order to fix this, remove the pool locking from the refcount helpers,
> and move all the logic to the buddy allocator. This will simplify the
> removal of the list node from struct hyp_page in a later patch.
Is there any chance some documentation could be added so that we have
a record of what the locking boundaries are? Something along the line
of what we have in arch/arm64/kvm/vgic/vgic.c, for example.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-06-01 12:12 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-27 12:51 [PATCH 0/7] KVM: arm64: Reduce hyp_vmemmap overhead Quentin Perret
2021-05-27 12:51 ` [PATCH 1/7] KVM: arm64: Move hyp_pool locking out of refcount helpers Quentin Perret
2021-06-01 12:02 ` Marc Zyngier [this message]
2021-06-01 13:31 ` Quentin Perret
2021-05-27 12:51 ` [PATCH 2/7] KVM: arm64: Use refcount at hyp to check page availability Quentin Perret
2021-05-27 12:51 ` [PATCH 3/7] KVM: arm64: Remove list_head from hyp_page Quentin Perret
2021-06-01 14:38 ` Marc Zyngier
2021-06-01 15:48 ` Quentin Perret
2021-06-01 17:41 ` Marc Zyngier
2021-06-02 9:23 ` Quentin Perret
2021-05-27 12:51 ` [PATCH 4/7] KVM: arm64: Unify MMIO and mem host stage-2 pools Quentin Perret
2021-05-27 12:51 ` [PATCH 5/7] KVM: arm64: Remove hyp_pool pointer from struct hyp_page Quentin Perret
2021-06-01 15:00 ` Marc Zyngier
2021-05-27 12:51 ` [PATCH 6/7] KVM: arm64: Use less bits for hyp_page order Quentin Perret
2021-05-27 12:51 ` [PATCH 7/7] KVM: arm64: Use less bits for hyp_page refcount Quentin Perret
2021-06-01 15:21 ` Marc Zyngier
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