linux-kernel - Re: [PATCH 2/2] mm/hmm: hmm_range

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Message-ID: <f5c1f198-4bdd-3c23-428f-764f894b9997@nvidia.com>
Date:   Tue, 27 Aug 2019 13:16:13 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <nouveau@...ts.freedesktop.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 2/2] mm/hmm: hmm_range_fault() infinite loop


On 8/27/19 11:41 AM, Jason Gunthorpe wrote:
> On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:
> 
>> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
>>   mm/hmm.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/mm/hmm.c b/mm/hmm.c
>> index 29371485fe94..4882b83aeccb 100644
>> +++ b/mm/hmm.c
>> @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
>>   	hmm_vma_walk->last = addr;
>>   	i = (addr - range->start) >> PAGE_SHIFT;
>>   
>> +	if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE))
>> +		return -EPERM;
> 
> Can walk->vma be NULL here? hmm_vma_do_fault() touches it
> unconditionally.
> 
> Jason
> 
walk->vma can be NULL. hmm_vma_do_fault() no longer touches it
unconditionally, that is what the preceding patch fixes.
I suppose I could change hmm_vma_walk_hole_() to check for NULL
and fill in the pfns[] array, I just chose to handle it in
hmm_vma_do_fault().