Messages in this thread | | | Date | Wed, 26 Jul 2000 11:56:55 +0100 (BST) | From | James Sutherland <> | Subject | Re: Direct access to hardware |
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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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