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

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Date:   Fri, 31 Aug 2018 16:11:37 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "\"eric.auger.pro"@gmail.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, 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

Hi Jean-Philippe,

On 08/31/2018 03:20 PM, Jean-Philippe Brucker wrote:
> 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)

Yep this works with my setup but I was waiting for such kind of comments
to turn this prototype into something more "production level" ;-) Did
you send anything upstream, related to this branch?

Thanks

Eric
> 
> Thanks,
> Jean
>