linux-kernel - Re: [PATCHv8 00/11] Linear Address Masking enabling

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Date:   Tue, 20 Sep 2022 14:57:04 +0000
From:   Ashok Raj <ashok_raj@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCHv8 00/11] Linear Address Masking enabling

On Tue, Sep 20, 2022 at 10:14:54AM -0300, Jason Gunthorpe wrote:
> On Thu, Sep 15, 2022 at 08:28:58PM +0300, Kirill A. Shutemov wrote:
> 
> > @@ -31,7 +33,17 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
> >  	    min == 0 || max < min)
> >  		return -EINVAL;
> >  
> > +	/* Serialize against address tagging enabling */
> > +	if (mmap_write_lock_killable(mm))
> > +		return -EINTR;
> > +
> > +	if (!arch_can_alloc_pasid(mm)) {
> > +		mmap_write_unlock(mm);
> > +		return -EBUSY;
> > +	}
> 
> This has nothing to do with "allocating pasid"
> 
> Rather should be: "is the CPU page table compatible with the IOMMU HW
> page table walker"

Thanks Jason, this certainly looks like a more logical way to look at it
rather than the functional association of allocating pasids. 

> 
> For this I would rather have a function that queries the format of the
> page table under the mm_struct and we have enum values like
> INTEL_NORMAL and INTEL_LAM as possible values.
> 
> The iommu driver will block incompatible page table formats, and when
> it starts up it should assert something that blocks changing the
> format.
> 
> Jason
>