linux-kernel - Re: [PATCH 5/8] x86/mmu: Add mm-based PASID refcounting

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Date:   Thu, 30 Sep 2021 00:44:00 +0000
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.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 5/8] x86/mmu: Add mm-based PASID refcounting

Hi, Baolu,

On Thu, Sep 23, 2021 at 01:43:32PM +0800, Lu Baolu wrote:
> On 9/21/21 3:23 AM, Fenghua Yu wrote:
> > +void pasid_put(struct task_struct *tsk, struct mm_struct *mm)
> > +{
> > +	if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> > +		return;
> > +
> > +	/*
> > +	 * Nothing to do if this task doesn't have a reference to the PASID.
> > +	 */
> > +	if (tsk->has_valid_pasid) {
> > +		mutex_lock(&pasid_mutex);
> > +		/*
> > +		 * The PASID's reference was taken during fix up. Release it
> > +		 * now. If the reference count is 0, the PASID is freed.
> > +		 */
> > +		iommu_sva_free_pasid(mm);
> > +		mutex_unlock(&pasid_mutex);
> > +	}
> > +}
> > 
> 
> It looks odd that both __fixup_pasid_exception() and pasid_put() are
> defined in the vendor IOMMU driver, but get called in the arch/x86
> code.
> 
> Is it feasible to move these two helpers to the files where they are
> called? The IA32_PASID MSR fixup and release are not part of the IOMMU
> implementation.

Sure. The functions will be removed in the next version. And new functions
will not be called in IOMMU driver.

Thanks.

-Fenghua