linux-kernel - Re: [PATCH v2 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

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Message-ID: <87ee4w6g1n.ffs@tglx>
Date:   Mon, 24 Jan 2022 21:21:24 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v2 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit

On Fri, Dec 17 2021 at 22:01, Fenghua Yu wrote:
> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
> index bd41405d34e9..ee2294e02716 100644
> --- a/drivers/iommu/iommu-sva-lib.c
> +++ b/drivers/iommu/iommu-sva-lib.c
> @@ -18,8 +18,7 @@ static DECLARE_IOASID_SET(iommu_sva_pasid);
>   *
>   * Try to allocate a PASID for this mm, or take a reference to the existing one
>   * provided it fits within the [@min, @max] range. On success the PASID is
> - * available in mm->pasid, and must be released with iommu_sva_free_pasid().
> - * @min must be greater than 0, because 0 indicates an unused mm->pasid.
> + * available in mm->pasid and will be available for the lifetime of the mm.
>   *
>   * Returns 0 on success and < 0 on error.
>   */
> @@ -33,38 +32,24 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
>  		return -EINVAL;
>  
>  	mutex_lock(&iommu_sva_lock);
> -	if (mm->pasid) {
> -		if (mm->pasid >= min && mm->pasid <= max)
> -			ioasid_get(mm->pasid);
> -		else
> +	/* Is a PASID already associated with this mm? */
> +	if (pasid_valid(mm->pasid)) {
> +		if (mm->pasid < min || mm->pasid >= max)
>  			ret = -EOVERFLOW;
> -	} else {
> -		pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> -		if (pasid == INVALID_IOASID)
> -			ret = -ENOMEM;
> -		else
> -			mm->pasid = pasid;
> +		goto out;
>  	}
> +
> +	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> +	if (!pasid_valid(pasid))
> +		ret = -ENOMEM;
> +	else
> +		mm_pasid_get(mm, pasid);

Hrm. This is odd.

> +/* Associate a PASID with an mm_struct: */
> +static inline void mm_pasid_get(struct mm_struct *mm, u32 pasid)
> +{
> +	mm->pasid = pasid;
> +}

This does not get anything. It sets the allocated PASID in the mm. The
refcount on the PASID was already taken by the allocation. So this
should be mm_pasid_set() or mm_pasid_install(), right?

Thanks,

        tglx