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

From: Fenghua Yu <fenghua.yu@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	iommu@lists.linux-foundation.org, x86 <x86@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit
Date: Mon, 24 Jan 2022 12:33:12 -0800	[thread overview]
Message-ID: <Ye8NCAKoGF/AsLfs@otcwcpicx3.sc.intel.com> (raw)
In-Reply-To: <87ee4w6g1n.ffs@tglx>

Hi, Thomas,

On Mon, Jan 24, 2022 at 09:21:24PM +0100, Thomas Gleixner wrote:
> 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?

Ok. Will change mm_pasid_get() to mm_pasid_set().

Thank you very much for your review!

-Fenghua