> Ouch, this shouldn't be allowed in user space! WBINVD is a privileged
> instruction. Do we leak privileges to user land??? Please check if your
> execution mode (privilege ring) is correct there.
No, I rather meant a kernel-mode program that was controlled from the user
space. Sorry for upsetting you.
But indeed, wbinvd is devastating if you can execute it, causing
> typically around 300 us latencies, at worst even milliseconds
> (cache-size and state dependent)!
If I recall correctly, some of the Linux AGP GART drivers use(d?) it.
This raises another interesting question: to what extent is the x86 actually
a viable and dependable realtime platform, with its SMI's and highly
uncontrollable caching architecture ? How would VT-based solutions compare ?
(BTW Intel should really have implemented a feature to use parts of the
cache as SRAM.)
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