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Re: User applications

To: "Kevin D. Kissell" <>
Subject: Re: User applications
From: "Maciej W. Rozycki" <>
Date: Mon, 8 Jan 2001 16:07:31 +0100 (MET)
Cc:, Carsten Langgaard <>, Michael Shmulevich <>
In-reply-to: <00d801c0797d$5cc410c0$0deca8c0@Ulysses>
Organization: Technical University of Gdansk
Reply-to: "Maciej W. Rozycki" <>
On Mon, 8 Jan 2001, Kevin D. Kissell wrote:

> Back in the Ancient Old Days of System V, every architecture
> had an architecture-specific system call entry, the first parameter
> of which expressed what needed to be done.  Do we have
> such a thing in Linux?   That would be the logical place to
> things like cache flush and the atomic operations that were
> being discussed here a couple of weeks ago.

 The only case caches need to be synchronized is modifying some code.  The
ptrace syscall does it automatically for text writes -- it's needed and
used by gdb to set breakpoints, for example.  For other code there is
cacheflush() which allows you to flush a cache range relevant to a given
virtual address (I see it's not implemented very well at the moment).

 Obviously, you don't want to allow unprivileged users to flush caches as
a whole as it could lead to a DoS. 

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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