On 25 Jul 2000, Krzysztof Halasa wrote:
> James Sutherland <jas88@cam.ac.uk> writes:
>
> > On Tue, 25 Jul 2000, Stuart MacDonald wrote:
> >
> > > Which is exactly the point. The hard drives should be checking for
> > > invalid ATA commands in hardware, right in the drive, preventing
> > > damage from bad commands. Putting a filter into the kernel is not
> > > the right fix.
> >
> > As with some of the Intel CPU bugs, the problem is NOT "invalid ATA
> > commands" - it's a matter of VALID commands which are dangerous. FDIV on
> > early Pentiums isn't an invalid instruction - it just produces the wrong
> > results at times. So the SOFTWARE must do something to avoid this - either
> > that, or you need to replace the hardware, which isn't desirable. You do
> > something in the OS to prevent these problem commands being used.
>
> So what does the kernel (can) do to prevent this problem on defective
> pentiums?
Trap the defective instructions, and implement a replacement instruction
in software. On later Intel CPUs, you can sometimes use a microcode update
to fix it - this also requires OS intervention.
Either way, essentially you tell the OS to block the duff instructions,
and it does so.
James.
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