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

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Message-ID: <c58adc13-306a-8df8-19e1-27f834b3a7c9@linux.intel.com>
Date:   Sat, 16 Jan 2021 09:20:16 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     baolu.lu@...ux.intel.com, 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

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;
+}

Best regards,
baolu