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

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Date:   Fri, 15 Jan 2021 07:49:47 +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 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.

> 
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c  | 20 ++++++++++++++++++++
>>   drivers/iommu/virtio-iommu.c |  9 +++++++++
>>   include/linux/iommu.h        |  1 +
>>   3 files changed, 30 insertions(+)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index cb205a04fe4c..8eb022d0e8aa 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
>>   	return ret;
>>   }
>>
>> +static inline bool caching_mode_enabled(void)
>> +{
> 
> Kernel coding style is not in favour of inline functions in *.c files.

Yes, agreed.

Best regards,
baolu

> 
>> +	struct dmar_drhd_unit *drhd;
>> +	struct intel_iommu *iommu;
>> +	bool ret = false;
>> +
>> +	rcu_read_lock();
>> +	for_each_active_iommu(iommu, drhd) {
>> +		if (cap_caching_mode(iommu->cap)) {
>> +			ret = true;
>> +			break;
>> +		}
>> +	}
>> +	rcu_read_unlock();
>> +
>> +	return ret;
>> +}
>> +
>>   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;
>>   }
>> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
>> index 2bfdd5734844..719793e103db 100644
>> --- a/drivers/iommu/virtio-iommu.c
>> +++ b/drivers/iommu/virtio-iommu.c
>> @@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
>>   	return iommu_fwspec_add_ids(dev, args->args, 1);
>>   }
>>
>> +static bool viommu_capable(enum iommu_cap cap)
>> +{
>> +	if (cap == IOMMU_CAP_VIOMMU)
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>>   static struct iommu_ops viommu_ops = {
>> +	.capable		= viommu_capable,
>>   	.domain_alloc		= viommu_domain_alloc,
>>   	.domain_free		= viommu_domain_free,
>>   	.attach_dev		= viommu_attach_dev,
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index b95a6f8db6ff..1d24be667a03 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -94,6 +94,7 @@ enum iommu_cap {
>>   					   transactions */
>>   	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
>>   	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
>> +	IOMMU_CAP_VIOMMU,		/* IOMMU can declar running in a VM */
>>   };
>>
>>   /*
>> --
>> 2.25.1
>>