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From: Ming Lin <minggr@gmail.com>
To: Hugh Dickins <hughd@google.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Simon Ser <contact@emersion.fr>
Cc: Peter Xu <peterx@redhat.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Dan Williams <dan.j.williams@intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Will Deacon <will@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	David Herrmann <dh.herrmann@gmail.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Greg Kroah-Hartman <greg@kroah.com>,
	"tytso@mit.edu" <tytso@mit.edu>
Subject: Re: Sealed memfd & no-fault mmap
Date: Mon, 31 May 2021 14:13:28 -0700	[thread overview]
Message-ID: <e7454046-c071-888d-f673-276f9c24d9d3@gmail.com> (raw)
In-Reply-To: <36fc2485-11f1-5252-904d-f26b63a6cd58@gmail.com>

On 5/29/2021 4:36 PM, Ming Lin wrote:
> On 5/29/2021 1:15 PM, Hugh Dickins wrote:
> 
>>
>> I believe the correct behaviour would be to unmap the nofault page
>> then, allowing the proper page to be faulted in after.  That is
>> certainly doable (the old mm/filemap_xip.c used to do so), but might
>> get into some awkward race territory, with filesystem dependence
>> (reminiscent of hole punch, in reverse).  shmem could operate that
>> way, and be the better for it: but I wouldn't want to add that,
>> without also cleaning away all the shmem_recalc_inode() stuff.

OK, I borrowed code from filemap_xip.c and implemented this behavior.

Simon,

Before I send out the patches for review, would you mind have a quick test?
https://github.com/minggr/linux, branch shmem_no_sigbus

In Wayland compositors, you only need to pass in MAP_NOSIGBUS in mmap().
For example,

//fd should be received from Wayland compositors client
#define MAP_NOSIGBUS    0x200000
addr = mmap(NULL, size, PROT_READ, MAP_SHARED|MAP_NOSIGBUS, fd, offset)

Thanks,
Ming


  reply	other threads:[~2021-05-31 21:13 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-27  8:24 Sealed memfd & no-fault mmap Simon Ser
2021-04-27 16:51 ` Linus Torvalds
2021-04-27 16:51   ` Linus Torvalds
2021-04-29 15:48   ` Kirill A. Shutemov
2021-04-29 18:38     ` Peter Xu
2021-05-04  9:29       ` Simon Ser
2021-05-04 16:08         ` Linus Torvalds
2021-05-04 16:08           ` Linus Torvalds
2021-05-05 10:21           ` Simon Ser
2021-05-05 18:42             ` Linus Torvalds
2021-05-05 18:42               ` Linus Torvalds
2021-05-28 17:07               ` Lin, Ming
2021-05-29  1:03                 ` Linus Torvalds
2021-05-29  1:03                   ` Linus Torvalds
2021-05-29  7:31                   ` Lin, Ming
2021-05-29 15:44                     ` Linus Torvalds
2021-05-29 15:44                       ` Linus Torvalds
2021-05-29 20:15                       ` Hugh Dickins
2021-05-29 20:15                         ` Hugh Dickins
2021-05-29 23:36                         ` Ming Lin
2021-05-31 21:13                           ` Ming Lin [this message]
2021-06-01  6:24                             ` Linus Torvalds
2021-06-01  6:24                               ` Linus Torvalds
2021-06-01  7:08                               ` Ming Lin
2021-06-03 13:01                                 ` Simon Ser
2021-06-03 20:07                                   ` Ming Lin
2021-06-03 20:49                                     ` Simon Ser
2021-06-03 13:14                         ` Simon Ser
2021-06-03 13:57                           ` Matthew Wilcox
2021-06-03 14:48                             ` Simon Ser

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