linux-kernel - Re: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA PASIDs

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Date:   Tue, 28 Mar 2023 13:11:12 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org
Cc:     baolu.lu@...ux.intel.com, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: Re: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA
 PASIDs

On 3/28/23 7:21 AM, Jacob Pan wrote:
> Devices that use Intel ENQCMD to submit work must use global PASIDs in
> that the PASID are stored in a per CPU MSR. When such device need to
> submit work for in-kernel DMA with PASID, it must allocate PASIDs from
> the same global number space to avoid conflict.
> 
> This patch introduces IOMMU SVA APIs to reserve and release global PASIDs.
> It is expected that device drivers will use the allocated PASIDs to attach
> to appropriate IOMMU domains for use.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>   drivers/iommu/iommu-sva.c | 33 +++++++++++++++++++++++++++++++++
>   include/linux/iommu.h     | 14 ++++++++++++++
>   2 files changed, 47 insertions(+)
> 
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index c434b95dc8eb..84b9de84b3e0 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -148,6 +148,39 @@ u32 iommu_sva_get_pasid(struct iommu_sva *handle)
>   }
>   EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);
>   
> +/**
> + * @brief
> + *	Reserve a PASID from the SVA global number space.
> + *
> + * @param min starting range, inclusive
> + * @param max ending range, inclusive
> + * @return The reserved PASID on success or IOMMU_PASID_INVALID on failure.
> + */
> +ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max)
> +{
> +	int ret;
> +
> +	if (!pasid_valid(min) || !pasid_valid(max) ||
> +	    min == 0 || max < min)

I still think we should make "min == 0" a valid case. The ARM/AMD/Intel
drivers should reserve PASID 0 for special usage with this interface.

Probably we should also make "min == max" a valid case. Both @min and
@max are inclusive.

> +		return IOMMU_PASID_INVALID;
> +
> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_KERNEL);
> +	if (ret < 0)
> +		return IOMMU_PASID_INVALID;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_reserve_pasid);
> +
> +void iommu_sva_release_pasid(ioasid_t pasid)
> +{
> +	if (!pasid_valid(pasid))

The caller should never release an invalid pasid. So perhaps,

	if (WARN_ON(!pasid_valid(pasid)))
		return;

to discover bugs during development.

> +		return;
> +
> +	ida_free(&iommu_global_pasid_ida, pasid);
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_release_pasid);
> +
>   /*
>    * I/O page fault handler for SVA
>    */
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 54f535ff9868..0471089dc1d0 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -1187,6 +1187,9 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>   					struct mm_struct *mm);
>   void iommu_sva_unbind_device(struct iommu_sva *handle);
>   u32 iommu_sva_get_pasid(struct iommu_sva *handle);
> +ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max);
> +void iommu_sva_release_pasid(ioasid_t pasid);
> +
>   #else
>   static inline struct iommu_sva *
>   iommu_sva_bind_device(struct device *dev, struct mm_struct *mm)
> @@ -1202,6 +1205,17 @@ static inline u32 iommu_sva_get_pasid(struct iommu_sva *handle)
>   {
>   	return IOMMU_PASID_INVALID;
>   }
> +
> +static inline ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max)
> +{
> +	return IOMMU_PASID_INVALID;
> +}
> +
> +static inline void iommu_sva_release_pasid(ioasid_t pasid)
> +{
> +
> +}
> +
>   static inline void mm_pasid_init(struct mm_struct *mm) {}
>   static inline void mm_pasid_drop(struct mm_struct *mm) {}
>   #endif /* CONFIG_IOMMU_SVA */

Best regards,
baolu