From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>, Arnd Bergmann <arnd@arndb.de>,
linux-nvdimm@lists.01.org, linux-api@vger.kernel.org,
linux-xfs@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-ext4@vger.kernel.org
Subject: Re: [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
Date: Tue, 24 Oct 2017 15:08:08 +0200 [thread overview]
Message-ID: <20171024130808.GC8556@quack2.suse.cz> (raw)
In-Reply-To: <20171020072707.GA18000@infradead.org>
On Fri 20-10-17 00:27:07, Christoph Hellwig wrote:
> > if (file) {
> > struct inode *inode = file_inode(file);
> > + unsigned long flags_mask = file->f_op->mmap_supported_flags;
> > +
> > + if (!flags_mask)
> > + flags_mask = LEGACY_MAP_MASK;
> >
> > switch (flags & MAP_TYPE) {
> > case MAP_SHARED:
> > + /*
> > + * Silently ignore unsupported flags - MAP_SHARED has
> > + * traditionally behaved like that and we don't want
> > + * to break compatibility.
> > + */
> > + flags &= flags_mask;
> > + /*
> > + * Force use of MAP_SHARED_VALIDATE with non-legacy
> > + * flags. E.g. MAP_SYNC is dangerous to use with
> > + * MAP_SHARED as you don't know which consistency model
> > + * you will get.
> > + */
> > + flags &= LEGACY_MAP_MASK;
> > + /* fall through */
> > + case MAP_SHARED_VALIDATE:
> > + if (flags & ~flags_mask)
> > + return -EOPNOTSUPP;
>
> Hmmm. I'd expect this to worth more like:
>
> case MAP_SHARED:
> /* Ignore all new flags that need validation: */
> flags &= LEGACY_MAP_MASK;
> /*FALLTHROUGH*/
> case MAP_SHARED_VALIDATE:
> if (flags & ~file->f_op->mmap_supported_flags)
> return -EOPNOTSUPP;
>
> with the legacy mask always implicitly support as indicated in my
> comment to the XFS patch.
I was thinking about this. Originally I thought that mmap_supported_flags
would allow also to declare some legacy flags as unsupported and also it
seemed as a nicer symmetric interface to me. But I guess the need to mask
out legacy flags is mostly theoretical so I'm fine giving that up. So I'll
change this as you suggest.
> Although even the ignoring in MAP_SHARED seems dangerous, but I guess
> we need that to keep strict backwards compatibility. In world I'd
> rather do
>
> case MAP_SHARED:
> if (flags & ~LEGACY_MAP_MASK)
> return -EINVAL;
Yes, I think just ignoring new flags for MAP_SHARED is safer...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm
WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-nvdimm@lists.01.org, linux-api@vger.kernel.org,
linux-xfs@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
linux-ext4@vger.kernel.org
Subject: Re: [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
Date: Tue, 24 Oct 2017 15:08:08 +0200 [thread overview]
Message-ID: <20171024130808.GC8556@quack2.suse.cz> (raw)
In-Reply-To: <20171020072707.GA18000@infradead.org>
On Fri 20-10-17 00:27:07, Christoph Hellwig wrote:
> > if (file) {
> > struct inode *inode = file_inode(file);
> > + unsigned long flags_mask = file->f_op->mmap_supported_flags;
> > +
> > + if (!flags_mask)
> > + flags_mask = LEGACY_MAP_MASK;
> >
> > switch (flags & MAP_TYPE) {
> > case MAP_SHARED:
> > + /*
> > + * Silently ignore unsupported flags - MAP_SHARED has
> > + * traditionally behaved like that and we don't want
> > + * to break compatibility.
> > + */
> > + flags &= flags_mask;
> > + /*
> > + * Force use of MAP_SHARED_VALIDATE with non-legacy
> > + * flags. E.g. MAP_SYNC is dangerous to use with
> > + * MAP_SHARED as you don't know which consistency model
> > + * you will get.
> > + */
> > + flags &= LEGACY_MAP_MASK;
> > + /* fall through */
> > + case MAP_SHARED_VALIDATE:
> > + if (flags & ~flags_mask)
> > + return -EOPNOTSUPP;
>
> Hmmm. I'd expect this to worth more like:
>
> case MAP_SHARED:
> /* Ignore all new flags that need validation: */
> flags &= LEGACY_MAP_MASK;
> /*FALLTHROUGH*/
> case MAP_SHARED_VALIDATE:
> if (flags & ~file->f_op->mmap_supported_flags)
> return -EOPNOTSUPP;
>
> with the legacy mask always implicitly support as indicated in my
> comment to the XFS patch.
I was thinking about this. Originally I thought that mmap_supported_flags
would allow also to declare some legacy flags as unsupported and also it
seemed as a nicer symmetric interface to me. But I guess the need to mask
out legacy flags is mostly theoretical so I'm fine giving that up. So I'll
change this as you suggest.
> Although even the ignoring in MAP_SHARED seems dangerous, but I guess
> we need that to keep strict backwards compatibility. In world I'd
> rather do
>
> case MAP_SHARED:
> if (flags & ~LEGACY_MAP_MASK)
> return -EINVAL;
Yes, I think just ignoring new flags for MAP_SHARED is safer...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
To: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>,
Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>,
linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
Date: Tue, 24 Oct 2017 15:08:08 +0200 [thread overview]
Message-ID: <20171024130808.GC8556@quack2.suse.cz> (raw)
In-Reply-To: <20171020072707.GA18000-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
On Fri 20-10-17 00:27:07, Christoph Hellwig wrote:
> > if (file) {
> > struct inode *inode = file_inode(file);
> > + unsigned long flags_mask = file->f_op->mmap_supported_flags;
> > +
> > + if (!flags_mask)
> > + flags_mask = LEGACY_MAP_MASK;
> >
> > switch (flags & MAP_TYPE) {
> > case MAP_SHARED:
> > + /*
> > + * Silently ignore unsupported flags - MAP_SHARED has
> > + * traditionally behaved like that and we don't want
> > + * to break compatibility.
> > + */
> > + flags &= flags_mask;
> > + /*
> > + * Force use of MAP_SHARED_VALIDATE with non-legacy
> > + * flags. E.g. MAP_SYNC is dangerous to use with
> > + * MAP_SHARED as you don't know which consistency model
> > + * you will get.
> > + */
> > + flags &= LEGACY_MAP_MASK;
> > + /* fall through */
> > + case MAP_SHARED_VALIDATE:
> > + if (flags & ~flags_mask)
> > + return -EOPNOTSUPP;
>
> Hmmm. I'd expect this to worth more like:
>
> case MAP_SHARED:
> /* Ignore all new flags that need validation: */
> flags &= LEGACY_MAP_MASK;
> /*FALLTHROUGH*/
> case MAP_SHARED_VALIDATE:
> if (flags & ~file->f_op->mmap_supported_flags)
> return -EOPNOTSUPP;
>
> with the legacy mask always implicitly support as indicated in my
> comment to the XFS patch.
I was thinking about this. Originally I thought that mmap_supported_flags
would allow also to declare some legacy flags as unsupported and also it
seemed as a nicer symmetric interface to me. But I guess the need to mask
out legacy flags is mostly theoretical so I'm fine giving that up. So I'll
change this as you suggest.
> Although even the ignoring in MAP_SHARED seems dangerous, but I guess
> we need that to keep strict backwards compatibility. In world I'd
> rather do
>
> case MAP_SHARED:
> if (flags & ~LEGACY_MAP_MASK)
> return -EINVAL;
Yes, I think just ignoring new flags for MAP_SHARED is safer...
Honza
--
Jan Kara <jack-IBi9RG/b67k@public.gmane.org>
SUSE Labs, CR
next prev parent reply other threads:[~2017-10-24 13:04 UTC|newest]
Thread overview: 121+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-19 12:57 [PATCH 0/17 v4] dax, ext4, xfs: Synchronous page faults Jan Kara
2017-10-19 12:57 ` Jan Kara
2017-10-19 12:57 ` Jan Kara
2017-10-19 12:57 ` Jan Kara
2017-10-19 12:57 ` Jan Kara
2017-10-19 12:58 ` [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 16:48 ` Dan Williams
2017-10-19 16:48 ` Dan Williams
2017-10-19 16:48 ` Dan Williams
2017-10-20 7:27 ` Christoph Hellwig
2017-10-20 7:27 ` Christoph Hellwig
2017-10-24 13:08 ` Jan Kara [this message]
2017-10-24 13:08 ` Jan Kara
2017-10-24 13:08 ` Jan Kara
2017-10-19 12:58 ` [PATCH 02/17] mm: Remove VM_FAULT_HWPOISON_LARGE_MASK Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 03/17] dax: Simplify arguments of dax_insert_mapping() Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 04/17] dax: Factor out getting of pfn out of iomap Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 05/17] dax: Create local variable for VMA in dax_iomap_pte_fault() Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 06/17] dax: Create local variable for vmf->flags & FAULT_FLAG_WRITE test Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 07/17] dax: Inline dax_insert_mapping() into the callsite Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 08/17] dax: Inline dax_pmd_insert_mapping() " Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 09/17] dax: Fix comment describing dax_iomap_fault() Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 10/17] dax: Allow dax_iomap_fault() to return pfn Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 11/17] dax: Allow tuning whether dax_insert_mapping_entry() dirties entry Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 12/17] mm: Define MAP_SYNC and VM_SYNC flags Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 13/17] dax, iomap: Add support for synchronous faults Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 14/17] dax: Implement dax_finish_sync_fault() Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 15/17] ext4: Simplify error handling in ext4_dax_huge_fault() Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 16/17] ext4: Support for synchronous DAX faults Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` [PATCH 17/17] xfs: support " Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 13:17 ` Christoph Hellwig
2017-10-19 13:17 ` Christoph Hellwig
2017-10-19 12:58 ` [PATCH] mmap.2: Add description of MAP_SHARED_VALIDATE and MAP_SYNC Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-19 12:58 ` Jan Kara
2017-10-20 21:47 ` Ross Zwisler
2017-10-20 21:47 ` Ross Zwisler
2017-10-20 21:47 ` Ross Zwisler
2017-10-24 13:27 ` Jan Kara
2017-10-24 13:27 ` Jan Kara
2017-10-24 13:27 ` Jan Kara
2017-10-24 14:55 ` Ross Zwisler
2017-10-24 14:55 ` Ross Zwisler
2017-10-24 14:55 ` Ross Zwisler
2017-10-24 15:23 [PATCH 0/17 v5] dax, ext4, xfs: Synchronous page faults Jan Kara
2017-10-24 15:23 ` [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags Jan Kara
2017-10-24 15:23 ` Jan Kara
2017-10-24 15:23 ` Jan Kara
2017-10-24 15:23 ` Jan Kara
2017-10-24 15:23 ` Jan Kara
2017-10-24 21:21 ` Ross Zwisler
2017-10-24 21:21 ` Ross Zwisler
2017-10-24 21:21 ` Ross Zwisler
2017-10-24 21:21 ` Ross Zwisler
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