From: Philippe Gerum <rpm@xenomai.org>
To: Jesus Villena <j.villena@ecler.com>
Cc: "xenomai@lists.linux.dev" <xenomai@lists.linux.dev>
Subject: Re: [EVL] Problems writing to physical memory with mmap on oob context
Date: Wed, 27 Sep 2023 08:51:51 +0200 [thread overview]
Message-ID: <87y1gsm7as.fsf@xenomai.org> (raw)
In-Reply-To: <DB8PR10MB3706CC719B10DB6F15F7C64BF9C3A@DB8PR10MB3706.EURPRD10.PROD.OUTLOOK.COM>
Jesus Villena <j.villena@ecler.com> writes:
> Yes, that's what I understood!
>
> Anyway, I have made some progress: if I write something to the shared area (which is less than 4KB) before going to oob context, it works as expected!
>
> So, it seems to do with a page_fault the first time a write is issued in the shared area. Sorry, but I don't understand properly all complexity about accessing Linux virtual and physical memory, security, and protection.
>
This memory range may have copy-on-write semantics, which would explain
the major fault when first touched for update. It would make sense to
pre-fault this area in order to break COW early for it.
--
Philippe.
prev parent reply other threads:[~2023-09-27 6:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-26 11:21 [EVL] Problems writing to physical memory with mmap on oob context Jesus Villena
2023-09-26 14:15 ` Philippe Gerum
2023-09-26 15:40 ` Jesus Villena
2023-09-26 15:46 ` Philippe Gerum
2023-09-26 16:04 ` Jesus Villena
2023-09-27 6:51 ` Philippe Gerum [this message]
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