linux-kernel - Re: [PATCH v13 4/8] KVM: arm64: Introduce MTE VM feature

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Date:   Fri, 4 Jun 2021 15:05:44 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Steven Price <steven.price@....com>
Cc:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Dave Martin <Dave.Martin@....com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>, qemu-devel@...gnu.org,
        Juan Quintela <quintela@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Peter Maydell <peter.maydell@...aro.org>,
        Haibo Xu <Haibo.Xu@....com>, Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH v13 4/8] KVM: arm64: Introduce MTE VM feature

On Fri, Jun 04, 2021 at 01:51:38PM +0100, Steven Price wrote:
> On 04/06/2021 12:36, Catalin Marinas wrote:
> > On Fri, Jun 04, 2021 at 11:42:11AM +0100, Steven Price wrote:
> >> On 03/06/2021 17:00, Catalin Marinas wrote:
> >>> On Mon, May 24, 2021 at 11:45:09AM +0100, Steven Price wrote:
> >>>> @@ -971,8 +1007,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> >>>>  	if (writable)
> >>>>  		prot |= KVM_PGTABLE_PROT_W;
> >>>>  
> >>>> -	if (fault_status != FSC_PERM && !device)
> >>>> +	if (fault_status != FSC_PERM && !device) {
> >>>> +		ret = sanitise_mte_tags(kvm, pfn, vma_pagesize);
> >>>> +		if (ret)
> >>>> +			goto out_unlock;
> >>>
> >>> Maybe it was discussed in a previous version, why do we need this in
> >>> addition to kvm_set_spte_gfn()?
> >>
> >> kvm_set_spte_gfn() is only used for the MMU notifier path (e.g. if a
> >> memslot is changed by the VMM). For the initial access we will normally
> >> fault the page into stage 2 with user_mem_abort().
> > 
> > Right. Can we move the sanitise_mte_tags() call to
> > kvm_pgtable_stage2_map() instead or we don't have the all the
> > information needed?
> 
> I tried that before: kvm_pgtable_stage2_map() is shared with the
> hypervisor so sadly we can't go poking around in the host as this breaks
> on nVHE. I mentioned it in the v12 cover letter but it was in a wall of
> text:

Ah, I missed this in the cover letter (haven't read it).

So, apart from the nitpick with the early return for less indentation,
feel free to add:

Reviewed-by: Catalin Marinas <catalin.marinas@....com>