linux-kernel - Re: [RFC PATCH v2 26/26] KVM: arm64: Wrap the host with a stage 2

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Date:   Wed, 3 Feb 2021 16:11:47 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, android-kvm@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Fuad Tabba <tabba@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>
Subject: Re: [RFC PATCH v2 26/26] KVM: arm64: Wrap the host with a stage 2

On Fri, Jan 08, 2021 at 12:15:24PM +0000, Quentin Perret wrote:
> When KVM runs in protected nVHE mode, make use of a stage 2 page-table
> to give the hypervisor some control over the host memory accesses. At
> the moment all memory aborts from the host will be instantly idmapped
> RWX at stage 2 in a lazy fashion. Later patches will make use of that
> infrastructure to implement access control restrictions to e.g. protect
> guest memory from the host.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_cpufeature.h       |   2 +
>  arch/arm64/kernel/image-vars.h                |   3 +
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  33 +++
>  arch/arm64/kvm/hyp/nvhe/Makefile              |   2 +-
>  arch/arm64/kvm/hyp/nvhe/hyp-init.S            |   1 +
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c            |   6 +
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 191 ++++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/setup.c               |   6 +
>  arch/arm64/kvm/hyp/nvhe/switch.c              |   7 +-
>  arch/arm64/kvm/hyp/nvhe/tlb.c                 |   4 +-
>  10 files changed, 248 insertions(+), 7 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/mem_protect.c

[...]

> +void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
> +{
> +	enum kvm_pgtable_prot prot;
> +	u64 far, hpfar, esr, ipa;
> +	int ret;
> +
> +	esr = read_sysreg_el2(SYS_ESR);
> +	if (!__get_fault_info(esr, &far, &hpfar))
> +		hyp_panic();
> +
> +	prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W | KVM_PGTABLE_PROT_X;
> +	ipa = (hpfar & HPFAR_MASK) << 8;
> +	ret = host_stage2_map(ipa, PAGE_SIZE, prot);

Can we try to put down a block mapping if the whole thing falls within
memory?

Will