25 Jul
2014
25 Jul
'14
11:01 a.m.
From: Paul Birkel <pbirkel at gmail.com>
Intel started supporting a RAM patch area, I believe, after the Pentium bug
so that they could field-update during the low-level boot process to
(quietly!) overcome any similar problem in the future. Does anyone have
more specifics on this feature, and does this capability currently exist in
any of their more modern CPU architectures?
Intel still has the microcode patch functionality in (at least) their
mainline processors (Celeron, Pentium, Core, i-series and Xeon) and Atom.
The process is documented in section 9.11 of the Intel 64 and IA-32
Architectures Developer's Manual, Vol. 3A. Tl;dr: The patch can be loaded
at boot time by the BIOS, or later by the operating system, via writing the
updates virtual address to a privileged MSR called IA32_UCODE_WRITE.
BTW...as I recall (it's been a while), the big problem with the Pentium DIV
bug was that the error was in the hard-wired logic and couldn't be patched
by a microcode update.
KJ