linux-kernel - Re: [PATCHv16 11/17] x86/mm/iommu/sva: Make LAM and SVA mutually exclusive

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Date:   Mon, 3 Apr 2023 12:44:19 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv16 11/17] x86/mm/iommu/sva: Make LAM and SVA mutually
 exclusive

On Mon, Apr 03, 2023 at 08:18:57AM +0200, Dmitry Vyukov wrote:
> Hi Kirill,
> 
> ARCH_ENABLE_TAGGED_ADDR checks that task->mm == current->mm,
> shouldn't ARCH_FORCE_TAGGED_SVA check that as well?

Do you a particular race in mind? I cannot think of anything right away.

I guess we can add the check for consistency. But if there's a bug it is a
different story.

> Also it looks like currently to enable both LAM and SVA.
> LAM enabling checks for SVA, but SVA doesn't and both are not mutually
> exclusive.

For LAM we check SVM with mm_valid_pasid() && !test_bit() in
prctl_enable_tagged_addr().

For SVM we check for LAM with !mm_lam_cr3_mask() || test_bit() in
arch_pgtable_dma_compat() which called from iommu_sva_alloc_pasid().

Hm?


-- 
  Kiryl Shutsemau / Kirill A. Shutemov