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

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Message-ID: <20211105122557.GA2744544@nvidia.com>
Date:   Fri, 5 Nov 2021 09:25:57 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alistair Popple <apopple@...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 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

> 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