linux-kernel - Re: [PATCH v3 2/3] mm/migrate_device.c: Copy pte dirty bit to page

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Message-ID: <Ywjs/i4kIVlxZwpb@xz-m1.local>
Date:   Fri, 26 Aug 2022 11:55:42 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, Nadav Amit <nadav.amit@...il.com>,
        huang ying <huang.ying.caritas@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>, paulus@...abs.org,
        linuxppc-dev@...ts.ozlabs.org, stable@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH v3 2/3] mm/migrate_device.c: Copy pte dirty bit to page

On Fri, Aug 26, 2022 at 04:47:22PM +0200, David Hildenbrand wrote:
> > To me anon exclusive only shows this mm exclusively owns this page. I
> > didn't quickly figure out why that requires different handling on tlb
> > flushs.  Did I perhaps miss something?
> 
> GUP-fast is the magic bit, we have to make sure that we won't see new
> GUP pins, thus the TLB flush.
> 
> include/linux/mm.h:gup_must_unshare() contains documentation.

Hmm.. Shouldn't ptep_get_and_clear() (e.g., xchg() on x86_64) already
guarantees that no other process/thread will see this pte anymore
afterwards?

-- 
Peter Xu