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

From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>,
	Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v13 4/8] KVM: arm64: Introduce MTE VM feature
Date: Fri, 4 Jun 2021 15:05:44 +0100	[thread overview]
Message-ID: <20210604140544.GF31173@arm.com> (raw)
In-Reply-To: <2265cbf6-d643-9122-79a8-90198ea16c64@arm.com>

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@arm.com>