linux-kernel - Re: [PATCH v4 0/6] normalize IOMMU dma mode boot options

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Message-ID: <b20fd8a6-88ce-7d26-8eb0-ed9f095988a6@huawei.com>
Date:   Mon, 8 Apr 2019 09:14:42 +0800
From:   Hanjun Guo <guohanjun@...wei.com>
To:     Zhen Lei <thunder.leizhen@...wei.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        John Garry <john.garry@...wei.com>,
        "Robin Murphy" <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        "Joerg Roedel" <joro@...tes.org>, Jonathan Corbet <corbet@....net>,
        linux-doc <linux-doc@...r.kernel.org>,
        Sebastian Ott <sebott@...ux.ibm.com>,
        "Gerald Schaefer" <gerald.schaefer@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        x86 <x86@...nel.org>, linux-ia64 <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH v4 0/6] normalize IOMMU dma mode boot options

Hi Zhen,

On 2019/4/7 20:41, Zhen Lei wrote:
> As Robin Murphy's suggestion:
> "It's also not necessarily obvious to the user how this interacts with
> IOMMU_DEFAULT_PASSTHROUGH, so if we really do go down this route, maybe it
> would be better to refactor the whole lot into a single selection of something
> like IOMMU_DEFAULT_MODE anyway."
> 
> In this version, I tried to normalize the IOMMU dma mode boot options for all
> ARCHs. When IOMMU is enabled, there are 3 dma modes: paasthrough(bypass),
> lazy(mapping but defer the IOTLB invalidation), strict. But currently each
> ARCHs defined their private boot options, different with each other. For
> example, to enable/disable "passthrough", ARM64 use iommu.passthrough=1/0,
> X86 use iommu=pt/nopt, PPC/POWERNV use iommu=nobypass.
> 
> 
> Zhen Lei (6):
>   iommu: use iommu.dma_mode to replace iommu.passthrough and
>     iommu.strict
>   iommu: keep dma mode build options consistent with cmdline options
>   iommu: add iommu_default_dma_mode_get() helper
>   s390/pci: use common boot option iommu.dma_mode
>   powernv/iommu: use common boot option iommu.dma_mode
>   x86/iommu: use common boot option iommu.dma_mode

This will break systems using boot options as now, and I think
this is unacceptable. If you want to do so, just introduce iommu.dma_mode
on top of those iommu boot options with dma mode boot options unchanged,
and iommu.dma_mode is for all archs but compatible with them.

Thanks
Hanjun