linux-kernel - Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC

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Message-ID: <YNXXwvuErVnlHt+s@8bytes.org>
Date:   Fri, 25 Jun 2021 15:18:58 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     will@...nel.org, robin.murphy@....com, bjorn.andersson@...aro.org,
        ulf.hansson@...aro.org, adrian.hunter@...el.com,
        bhelgaas@...gle.com, john.garry@...wei.com, robdclark@...omium.org,
        quic_c_gdjako@...cinc.com, saravanak@...gle.com,
        rajatja@...gle.com, saiprakash.ranjan@...eaurora.org,
        vbadigan@...eaurora.org, linux-mmc@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        iommu@...ts.linux-foundation.org, sonnyrao@...omium.org,
        joel@...lfernandes.org, Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krishna Reddy <vdumpa@...dia.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] iommu: Enable non-strict DMA on QCom SD/MMC

Hi Douglas,

On Thu, Jun 24, 2021 at 10:17:56AM -0700, Douglas Anderson wrote:
> The goal of this patch series is to get better SD/MMC performance on
> Qualcomm eMMC controllers and in generally nudge us forward on the
> path of allowing some devices to be in strict mode and others to be in
> non-strict mode.

So if I understand it right, this patch-set wants a per-device decision
about setting dma-mode to strict vs. non-strict.

I think we should get to the reason why strict mode is used by default
first. Is the default on ARM platforms to use iommu-strict mode by
default and if so, why?

The x86 IOMMUs use non-strict mode by default (yes, it is a security
trade-off).

Regards,

	Joerg