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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Mon, 14 Feb 2022 13:54:57 -0800
Message-ID: <CAC_TJvfgXSW9tQDHZ_1i31oBLKtGH6ymEDmoSemTa2ATwYkVMg@mail.gmail.com>
Subject: Re: [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements
To:     Marc Zyngier <maz@kernel.org>
Cc:     Will Deacon <will@kernel.org>, Quentin Perret <qperret@google.com>,
        Fuad Tabba <tabba@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Joey Gouly <joey.gouly@arm.com>,
        Peter Collingbourne <pcc@google.com>,
        Andrew Walbran <qwandor@google.com>,
        Andrew Scull <ascull@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, kvmarm@lists.cs.columbia.edu
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On Mon, Feb 14, 2022 at 3:41 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Thu, 10 Feb 2022 22:41:41 +0000,
> Kalesh Singh <kaleshsingh@google.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?

Hi Marc,

No technical reason. We hadn't thought of it from that perspective.
It's a good idea, I'll look into this and repost  a new version.

Thanks,
Kalesh

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