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From: Andrey Smirnov <andrew.smirnov@gmail.com>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Barebox List <barebox@lists.infradead.org>,
	Peter Mamonov <pmamonov@gmail.com>
Subject: Re: [PATCH v2 18/19] drivers: mem: Create file to access second half of 64-bit memory
Date: Fri, 1 Feb 2019 16:35:16 -0800	[thread overview]
Message-ID: <CAHQ1cqFDC-SJe+Lm29NQ+PhaS9yWCBj5zZVVprJJsTMyx1QBiA@mail.gmail.com> (raw)
In-Reply-To: <20190201074711.clrwidodo5hpqb7y@pengutronix.de>

On Thu, Jan 31, 2019 at 11:47 PM Sascha Hauer <s.hauer@pengutronix.de> wrote:
>
> On Thu, Jan 31, 2019 at 03:50:28PM +0300, Peter Mamonov wrote:
> > On Thu, Jan 31, 2019 at 01:54:52PM +0300, Peter Mamonov wrote:
> > > Hello, Andrey,
> > >
> > > > In order to allow access to second half of address space on 64-bit
> > > > machines, add code that creates /dev/highmem dedicated for that.
> > > >
> > > > Note that due to maximum file size being limited to MAX_LFS_FILESIZE
> > > > or 0x7fff_ffff_ffff_ffff bytes at addresses 0x7fff_ffff_ffff_ffff and
> > > > 0xffff_ffff_ffff_ffff cannot be access through /dev/mem and
> > > > /dev/hightmem correspondingly.
> > >
> > > Does it imply using `-s /dev/highmem` argument when accessing addresses beyond
> > > MAX_LFS_FILESIZE? That's not very convenient:
> > >
> > >     $ git grep -l /dev/mem
> > >     commands/crc.c
> > >     commands/digest.c
> > >     commands/disasm.c
> > >     commands/md.c
> > >     commands/memcmp.c
> > >     commands/memcpy.c
> > >     commands/memset.c
> > >     commands/mm.c
> > >     commands/mw.c
> >
> > I've forgotten to mention, that all meaningful MIPS64 virtual addresses
> > belong to the 2nd half of the address space. Except for user segment addresses
> > which are not used in barebox.
>
> In that case our only option seems to be to use an unsigned 64bit type
> for filesize. We would need an additional lseek like function which
> is able to reach the upper half of the address space and with regular
> lseek simply only the lower half would be reachable.
>
> Note that currently we don't seem to have a problem as even with Andreys
> series applied we can still 'md' the whole address space. The test if we
> lseek outside the file never triggers since the signed comparison of
> offset > f->size never evaluates to true for f->size == S64_MAX.
>

I am a bit confused by this statement. I agree The check for pos >
f->size won't evaluate to true if f->size == S64_MAX, but the pos < 0,
will. On my i.MX8MQ board with all but "drivers: mem: Create file to
access second half of 64-bit memory" applied I have:

barebox@ZII i.MX8MQ Ultra Zest Board:/ md -b 0x7ffffffffffffffe
7ffffffffffffffe: ff                                         .
barebox@ZII i.MX8MQ Ultra Zest Board:/ md -b 0x7fffffffffffffff
barebox@ZII i.MX8MQ Ultra Zest Board:/ md -b 0x8fffffffffffffff
lseek: Invalid argument
barebox@ZII i.MX8MQ Ultra Zest Board:/ md -b 0xfffffffffffffff0
lseek: Invalid argument

Thanks,
Andrey Smirnov

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  parent reply	other threads:[~2019-02-02  0:35 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-29  6:55 [PATCH v2 00/19] 32-bit lseek and /dev/mem fixes/improvements Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 01/19] commands: Move mem_parse_options() to lib/misc.c Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 02/19] commands: Get rid of mem_rw_buf Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 03/19] commands: Move /dev/mem driver to drivers/misc Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 04/19] nvmem: Do not use DEVFS_IS_CHARACTER_DEV Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 05/19] common: firmware: Don't use FILE_SIZE_STREAM directly Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 06/19] devfs: Fix incorrect error check for cdev->ops->lseek() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 07/19] fs: Update FILE position in lseek() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 08/19] fs: Drop trivial .lseek() implementaitons in FS drivers Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 09/19] devfs: Drop dev_lseek_default() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 10/19] fs: devfs: Change .lseek callbacks to return 'int' Andrey Smirnov
2019-02-04 14:32   ` Sascha Hauer
2019-01-29  6:55 ` [PATCH v2 11/19] fs: Do not use IS_ERR_VALUE() to validate offset in lseek() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 12/19] fs: Simplify new position calculation " Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 13/19] fs: Share code between mem_write()/mem_read() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 14/19] fs: Avoid division in mem_copy() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 15/19] fs: Report actual data processed by mem_copy() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 16/19] fs: Introduce mem_read_nofail() Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 17/19] commands: md: Do not use memmap() Andrey Smirnov
2019-02-04 13:57   ` Sascha Hauer
2019-02-04 19:35     ` Andrey Smirnov
2019-01-29  6:55 ` [PATCH v2 18/19] drivers: mem: Create file to access second half of 64-bit memory Andrey Smirnov
2019-01-29  8:48   ` Sascha Hauer
2019-01-29 20:40     ` Andrey Smirnov
2019-01-29 21:09       ` Sam Ravnborg
2019-01-31 10:54       ` Peter Mamonov
2019-01-31 12:50         ` Peter Mamonov
2019-02-01  7:47           ` Sascha Hauer
2019-02-01 10:25             ` Peter Mamonov
2019-02-02  1:07               ` Andrey Smirnov
2019-02-02  0:35             ` Andrey Smirnov [this message]
2019-02-04  7:40               ` Sascha Hauer
2019-01-31 20:17         ` Andrey Smirnov
2019-02-01 10:14           ` Peter Mamonov
2019-01-29  6:55 ` [PATCH v2 19/19] libfile: Fix incorrect lseek check in open_and_lseek() Andrey Smirnov

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