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

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Date:   Thu, 23 Sep 2021 16:36:50 +0200
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@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.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>
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 5/8] x86/mmu: Add mm-based PASID refcounting

On Mon, Sep 20 2021 at 19:23, Fenghua Yu wrote:
>  
> +#ifdef CONFIG_INTEL_IOMMU_SVM
> +void pasid_put(struct task_struct *tsk, struct mm_struct *mm);
> +#else
> +static inline void pasid_put(struct task_struct *tsk, struct mm_struct *mm) { }
> +#endif

This code is again defining that PASID is entirely restricted to
INTEL. It's true, that no other vendor supports this, but PASID is
a non-vendor specific concept.

Sticking this into INTEL code means that any other PASID implementation
has to rip it out again from INTEL code and make it a run time property.

The refcounting issue should be the same for all PASID mechanisms which
attach PASID to a mm. What's INTEL specific about that?

So can we pretty please do that correct right away?

Thanks,

        tglx