----- Original Message -----
From: "Maciej W. Rozycki" <firstname.lastname@example.org>
To: "Kevin D. Kissell" <email@example.com>
Cc: <firstname.lastname@example.org>; "Carsten Langgaard" <email@example.com>;
"Michael Shmulevich" <firstname.lastname@example.org>
Sent: Monday, January 08, 2001 4:07 PM
Subject: Re: User applications
> 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.
Which just happens to be the case under discussion here.
>The ptrace syscall does it automatically for text writes -- it's needed
> 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.
By that logic, we should not allow users to allocate more virtual
memory than there is physical memory in the system! A pathological
swap program is arguably far a far worse denial of service attack
than flushing the caches - so long as by "flush" we mean invalidate
with writeback (on copyback caches), of course.