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

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Date:   Tue, 20 Jul 2021 14:15:56 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
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 Tue, 20 Jul 2021 12:13:20 +0100,
Quentin Perret <qperret@...gle.com> wrote:
> 
> 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)?

Yup, all good points. I guess I could do the same in my other series
that parses the userspace PT to extract the level.

Thanks,

	M.

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