linux-kernel - Re: [PATCH v3 hmm 05/11] hmm: use mmu_notifier

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Date:   Wed, 14 Aug 2019 14:51:02 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, <linux-mm@...ck.org>
CC:     Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "Alex Deucher" <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        Dimitri Sivanich <sivanich@....com>,
        <dri-devel@...ts.freedesktop.org>, <amd-gfx@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <iommu@...ts.linux-foundation.org>,
        <intel-gfx@...ts.freedesktop.org>,
        Gavin Shan <shangw@...ux.vnet.ibm.com>,
        Andrea Righi <andrea@...terlinux.com>,
        Jason Gunthorpe <jgg@...lanox.com>
Subject: Re: [PATCH v3 hmm 05/11] hmm: use mmu_notifier_get/put for 'struct
 hmm'


On 8/6/19 4:15 PM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@...lanox.com>
> 
> This is a significant simplification, it eliminates all the remaining
> 'hmm' stuff in mm_struct, eliminates krefing along the critical notifier
> paths, and takes away all the ugly locking and abuse of page_table_lock.
> 
> mmu_notifier_get() provides the single struct hmm per struct mm which
> eliminates mm->hmm.
> 
> It also directly guarantees that no mmu_notifier op callback is callable
> while concurrent free is possible, this eliminates all the krefs inside
> the mmu_notifier callbacks.
> 
> The remaining krefs in the range code were overly cautious, drivers are
> already not permitted to free the mirror while a range exists.
> 
> Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>

Looks good.
Reviewed-by: Ralph Campbell <rcampbell@...dia.com>