----- Original Message ----- From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl> To: "Kevin D. Kissell" <kevink@mips.com> Cc: <linux-mips@oss.sgi.com>; "Carsten Langgaard" <carstenl@mips.com>; "Michael Shmulevich" <michaels@jungo.com> 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 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. 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.
