linux-kernel - Re: [RFC 09/13] iommu/smmuv3: Get prepared for nested stage support

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Message-ID: <538a2b88-dec5-a6fa-d918-486284eb56a9@arm.com>
Date:   Fri, 31 Aug 2018 14:20:34 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Eric Auger <eric.auger@...hat.com>, "\"eric.auger.pro"@gmail.com,
        eric.auger@...hat.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
        alex.williamson@...hat.com, jean-philippe.brucker@....com,
        jacob.jun.pan@...ux.intel.com, "yi.l.liu\""@linux.intel.com,
        will.deacon@....com, robin.murphy@....com
Cc:     marc.zyngier@....com, peter.maydell@...aro.org,
        christoffer.dall@....com
Subject: Re: [RFC 09/13] iommu/smmuv3: Get prepared for nested stage support

On 23/08/18 13:17, Eric Auger wrote:
>  	if (ste->s1_cfg) {
> -		BUG_ON(ste_live);

Scary! :) The current code assumes that it can make modifications to the
STE in any order and enable translation after a sync. So far I haven't
been able to find anything that violates this rule in the spec: "If
software modifies the structure while it is valid, it must not allow the
structure to enter an invalid intermediate state." So maybe it's fine,
though to be safe I would have started with disabling the STE
(http://www.linux-arm.org/git?p=linux-jpb.git;a=commitdiff;h=936e49f923e101c061269eadd5fa43fef819d2e9)

Thanks,
Jean