linux-kernel - Re: [PATCH] KVM: arm64: Always check the state from hyp_ack

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Message-Id: <173455738564.3742443.9773591453026966218.b4-ty@linux.dev>
Date: Wed, 18 Dec 2024 13:30:15 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: Marc Zyngier <maz@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Quentin Perret <qperret@...gle.com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Always check the state from hyp_ack_unshare()

On Thu, 28 Nov 2024 15:44:06 +0000, Quentin Perret wrote:
> There are multiple pKVM memory transitions where the state of a page is
> not cross-checked from the completer's PoV for performance reasons.
> For example, if a page is PKVM_PAGE_OWNED from the initiator's PoV,
> we should be guaranteed by construction that it is PKVM_NOPAGE for
> everybody else, hence allowing us to save a page-table lookup.
> 
> When it was introduced, hyp_ack_unshare() followed that logic and bailed
> out without checking the PKVM_PAGE_SHARED_BORROWED state in the
> hypervisor's stage-1. This was correct as we could safely assume that
> all host-initiated shares were directed at the hypervisor at the time.
> But with the introduction of other types of shares (e.g. for FF-A or
> non-protected guests), it is now very much required to cross check this
> state to prevent the host from running __pkvm_host_unshare_hyp() on a
> page shared with TZ or a non-protected guest.
> 
> [...]

Sorry for letting this one slip.

Applied to fixes, thanks!

[1/1] KVM: arm64: Always check the state from hyp_ack_unshare()
      https://git.kernel.org/kvmarm/kvmarm/c/985bb51f17ab

--
Best,
Oliver