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From: Peter Mamonov <pmamonov@gmail.com>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>,
	Barebox List <barebox@lists.infradead.org>
Subject: Re: [PATCH v2 18/19] drivers: mem: Create file to access second half of 64-bit memory
Date: Fri, 1 Feb 2019 13:25:21 +0300	[thread overview]
Message-ID: <20190201102520.33sxx2pdcawg2tlx@localhost.localdomain> (raw)
In-Reply-To: <20190201074711.clrwidodo5hpqb7y@pengutronix.de>

On Fri, Feb 01, 2019 at 08:47:11AM +0100, Sascha Hauer 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 can confirm that it is possible to enable access to the whole 64 bit address 
space via /dev/mem after adjusting /dev/mem size and eliminating checks for 
negative offset/pos in lseek(). Yet the proper approach seems to be to add a 
dedicated lseek implementation for /dev/mem, as in Linux.

Regards,
Peter

> 
> Sascha
> 
> -- 
> Pengutronix e.K.                           |                             |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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  reply	other threads:[~2019-02-01 10:25 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 [this message]
2019-02-02  1:07               ` Andrey Smirnov
2019-02-02  0:35             ` Andrey Smirnov
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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