linux-kernel - Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP

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Message-ID: <20210116083904.GN944463@unreal>
Date:   Sat, 16 Jan 2021 10:39:04 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     tglx@...utronix.de, ashok.raj@...el.com, kevin.tian@...el.com,
        dave.jiang@...el.com, megha.dey@...el.com, dwmw2@...radead.org,
        alex.williamson@...hat.com, bhelgaas@...gle.com,
        dan.j.williams@...el.com, will@...nel.org, joro@...tes.org,
        dmaengine@...r.kernel.org, eric.auger@...hat.com,
        jacob.jun.pan@...el.com, jgg@...lanox.com, kvm@...r.kernel.org,
        kwankhede@...dia.com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        maz@...nel.org, mona.hossain@...el.com, netanelg@...lanox.com,
        parav@...lanox.com, pbonzini@...hat.com, rafael@...nel.org,
        samuel.ortiz@...el.com, sanjay.k.kumar@...el.com,
        shahafs@...lanox.com, tony.luck@...el.com, vkoul@...nel.org,
        yan.y.zhao@...ux.intel.com, yi.l.liu@...el.com
Subject: Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

On Sat, Jan 16, 2021 at 09:20:16AM +0800, Lu Baolu wrote:
> Hi,
>
> On 2021/1/15 14:31, Leon Romanovsky wrote:
> > On Fri, Jan 15, 2021 at 07:49:47AM +0800, Lu Baolu wrote:
> > > Hi Leon,
> > >
> > > On 1/14/21 9:26 PM, Leon Romanovsky wrote:
> > > > On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote:
> > > > > Some vendor IOMMU drivers are able to declare that it is running in a VM
> > > > > context. This is very valuable for the features that only want to be
> > > > > supported on bare metal. Add a capability bit so that it could be used.
> > > >
> > > > And how is it used? Who and how will set it?
> > >
> > > Use the existing iommu_capable(). I should add more descriptions about
> > > who and how to use it.
> >
> > I want to see the code that sets this capability.
>
> Currently we have Intel VT-d and the virt-iommu setting this capability.
>
>  static bool intel_iommu_capable(enum iommu_cap cap)
>  {
>  	if (cap == IOMMU_CAP_CACHE_COHERENCY)
>  		return domain_update_iommu_snooping(NULL) == 1;
>  	if (cap == IOMMU_CAP_INTR_REMAP)
>  		return irq_remapping_enabled == 1;
> +	if (cap == IOMMU_CAP_VIOMMU)
> +		return caching_mode_enabled();
>
>  	return false;
>  }
>
> And,
>
> +static bool viommu_capable(enum iommu_cap cap)
> +{
> +	if (cap == IOMMU_CAP_VIOMMU)
> +		return true;
> +
> +	return false;
> +}

These two functions are reading this cap and not setting.
Where can I see code that does "cap = IOMMU_CAP_VIOMMU" and not "=="?

>
> Best regards,
> baolu