linux-kernel - Re: [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements

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Date:   Mon, 14 Feb 2022 11:41:14 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     will@...nel.org, qperret@...gle.com, tabba@...gle.com,
        surenb@...gle.com, kernel-team@...roid.com,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Joey Gouly <joey.gouly@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrew Walbran <qwandor@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements

On Thu, 10 Feb 2022 22:41:41 +0000,
Kalesh Singh <kaleshsingh@...gle.com> wrote:
> 
> This series is based on v5.17-rc3 and adds the following stack features to
> the KVM nVHE hypervisor:
> 
> == Hyp Stack Guard Pages ==
> 
> Based on the technique used by arm64 VMAP_STACK to detect overflow.
> i.e. the stack is aligned to twice its size which ensure that the 
> 'stack shift' bit of any valid SP is 0. The 'stack shift' bit can be
> tested in the exception entry to detect overflow without corrupting GPRs.

Having quickly parsed the code, this seems to only be effective for
pKVM and the EL2-allocated stack. Is there any technical reason not to
implement this for the much more common case of 'classic' KVM in nVHE
mode?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.