linux-kernel - Re: [PATCH] mm/hmm.c: Allow VM_MIXEDMAP to work with hmm_range

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Message-ID: <5535346.2Y9IAguWGx@nvdebian>
Date:   Mon, 8 Nov 2021 18:58:01 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     <akpm@...ux-foundation.org>, <jglisse@...hat.com>,
        <jhubbard@...dia.com>, <ziy@...dia.com>, <rcampbell@...dia.com>,
        <Felix.Kuehling@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/hmm.c: Allow VM_MIXEDMAP to work with hmm_range_fault

On Friday, 5 November 2021 11:25:57 PM AEDT Jason Gunthorpe wrote:
> On Thu, Nov 04, 2021 at 12:20:01PM +1100, Alistair Popple wrote:
> > hmm_range_fault() can be used instead of get_user_pages() for devices
> > which allow faulting however unlike get_user_pages() it will return an
> > error when used on a VM_MIXEDMAP range.
> > 
> > To make hmm_range_fault() more closely match get_user_pages() remove
> > this restriction. This requires dealing with the !ARCH_HAS_PTE_SPECIAL
> > case in hmm_vma_handle_pte(). Rather than replicating the logic of
> > vm_normal_page() call it directly and do a check for the zero pfn
> > similar to what get_user_pages() currently does.
> > 
> > Also add a test to hmm selftest to verify functionality.
> 
> Please add a fixes line

This has been the case since hmm_vma_get_pfns() was first introduced. Therefore
the fixes line is:

Fixes: da4c3c735ea4 ("mm/hmm/mirror: helper to snapshot CPU page table")

Should I send a v2 adding that tag or does Andrew normally pick these up along
with the Reviewed-by?

Thanks.

> > Signed-off-by: Alistair Popple <apopple@...dia.com>
> > ---
> >  lib/test_hmm.c                         | 24 +++++++++++++++
> >  mm/hmm.c                               |  5 +--
> >  tools/testing/selftests/vm/hmm-tests.c | 42 ++++++++++++++++++++++++++
> >  3 files changed, 69 insertions(+), 2 deletions(-)
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> 
> Jason
>