linux-kernel - Re: [PATCH 0/2] KVM: do not assume PTE is writable after follow

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Message-ID: <20210208185133.GW4718@ziepe.ca>
Date:   Mon, 8 Feb 2021 14:51:33 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Peter Xu <peterx@...hat.com>, dan.j.williams@...el.com
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/2] KVM: do not assume PTE is writable after follow_pfn

On Fri, Feb 05, 2021 at 01:14:11PM -0500, Peter Xu wrote:

> But I do have a question on why dax as the only user needs to pass in the
> notifier to follow_pte() for initialization.

Not sure either, why does DAX opencode something very much like
page_mkclean() with dax_entry_mkclean()?

Also it looks like DAX uses the wrong notifier, it calls
MMU_NOTIFY_CLEAR but page_mkclean_one() uses
MMU_NOTIFY_PROTECTION_PAGE for the same PTE modification sequence??

page_mkclean() has some technique to make the notifier have the right
size without becoming entangled in the PTL locks..

Jason