From: Wei Yang <richardw.yang@linux.intel.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>,
linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
linux-fsdevel@vger.kernel.org, Peter Xu <peterx@redhat.com>
Subject: Re: [PATCH] fs/userfaultfd.c: simplify the calculation of new_flags
Date: Sat, 5 Oct 2019 06:46:40 +0800 [thread overview]
Message-ID: <20191004224640.GC32588@richard> (raw)
In-Reply-To: <20191003004505.GE13922@redhat.com>
On Wed, Oct 02, 2019 at 08:45:05PM -0400, Andrea Arcangeli wrote:
>Hello,
>
>On Tue, Aug 06, 2019 at 01:38:59PM +0800, Wei Yang wrote:
>> Finally new_flags equals old vm_flags *OR* vm_flags.
>>
>> It is not necessary to mask them first.
>>
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>> fs/userfaultfd.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
>> index ccbdbd62f0d8..653d8f7c453c 100644
>> --- a/fs/userfaultfd.c
>> +++ b/fs/userfaultfd.c
>> @@ -1457,7 +1457,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
>> start = vma->vm_start;
>> vma_end = min(end, vma->vm_end);
>>
>> - new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
>> + new_flags = vma->vm_flags | vm_flags;
>> prev = vma_merge(mm, prev, start, vma_end, new_flags,
>> vma->anon_vma, vma->vm_file, vma->vm_pgoff,
>> vma_policy(vma),
>
>And then how do you clear the flags after the above?
>
>It must be possible to clear the flags (from
>UFFDIO_REGISTER_MODE_MISSING|UFFDIO_REGISTER_MODE_WP to only one set
>or invert).
>
>We have no WP support upstream yet, so maybe that's why it looks
>superfluous in practice, but in theory it isn't because it would then
>need to be reversed by Peter's (CC'ed) -wp patchset.
>
>The register code has already the right placeholder to support -wp and
>so it's better not to break them.
>
>I would recommend reviewing the uffd-wp support and working on testing
>the uffd-wp code instead of changing the above.
>
Sorry, I don't get your point. This change is valid to me even from arithmetic
point of view.
vm_flags == VM_UFFD_MISSING | VM_UFFD_WP
The effect of current code is clear these two bits then add them. This equals
to just add these two bits.
I am not sure which part I lost.
>Thanks,
>Andrea
--
Wei Yang
Help you, Help me
next prev parent reply other threads:[~2019-10-04 22:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-06 5:38 [PATCH] fs/userfaultfd.c: simplify the calculation of new_flags Wei Yang
2019-09-12 2:54 ` Wei Yang
2019-10-03 0:45 ` Andrea Arcangeli
2019-10-04 22:46 ` Wei Yang [this message]
2019-10-04 23:28 ` Andrea Arcangeli
2019-10-04 23:38 ` Wei Yang
2019-10-09 3:51 ` Peter Xu
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