linux-kernel - Re: [PATCH 04/16] KVM: arm64: Add MMIO checking infrastructure

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Date:   Tue, 20 Jul 2021 12:13:20 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org, will@...nel.org,
        dbrazdil@...gle.com, Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Shanker R Donthineni <sdonthineni@...dia.com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH 04/16] KVM: arm64: Add MMIO checking infrastructure

On Thursday 15 Jul 2021 at 17:31:47 (+0100), Marc Zyngier wrote:
> +struct s2_walk_data {
> +	kvm_pte_t	pteval;
> +	u32		level;
> +};
> +
> +static int s2_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> +		     enum kvm_pgtable_walk_flags flag, void * const arg)
> +{
> +	struct s2_walk_data *data = arg;
> +
> +	data->level = level;
> +	data->pteval = *ptep;
> +	return 0;
> +}
> +
> +/* Assumes mmu_lock taken */
> +static bool __check_ioguard_page(struct kvm_vcpu *vcpu, gpa_t ipa)
> +{
> +	struct s2_walk_data data;
> +	struct kvm_pgtable_walker walker = {
> +		.cb             = s2_walker,
> +		.flags          = KVM_PGTABLE_WALK_LEAF,
> +		.arg            = &data,
> +	};
> +
> +	kvm_pgtable_walk(vcpu->arch.hw_mmu->pgt, ALIGN_DOWN(ipa, PAGE_SIZE),
> +			 PAGE_SIZE, &walker);
> +
> +	/* Must be a PAGE_SIZE mapping with our annotation */
> +	return (BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(data.level)) == PAGE_SIZE &&
> +		data.pteval == MMIO_NOTE);

Nit: you could do this check in the walker directly and check the return
value of kvm_pgtable_walk() instead. That would allow to get rid of
struct s2_walk_data.

Also, though the compiler might be able to optimize, maybe simplify the
level check to level == (KVM_PGTABLE_MAX_LEVELS - 1)?

Thanks,
Quentin

> +}