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: <Ye8RmmKpJT8brmDE@otcwcpicx3.sc.intel.com>
Date:   Mon, 24 Jan 2022 12:52:42 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     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>,
        iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit

Hi, Thomas,

On Mon, Jan 24, 2022 at 09:36:00PM +0100, Thomas Gleixner wrote:
> On Mon, Jan 24 2022 at 21:21, Thomas Gleixner wrote:
> >
> > 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?
> 
> And as a result of all this ioasid_get() is now left without users...
> 
> Thanks,

Ah. This patch should remove ioasid_get(). So I will change this patch
as follows:

1. Remove ioasid_get() because it's not used any more when IOASID's
   refcount is set to 1 once the IOASID is allocated and is freed on mm exit.
2. Change mm_pasid_get() to mm_pasid_set().

Will that work?

Thanks.

-Fenghua