Messages in this thread | | | Date | Mon, 13 Apr 2009 09:44:59 +0300 | From | Avi Kivity <> | Subject | Re: [tip:x86/setup] x86, setup: "glove box" BIOS calls -- infrastructure |
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Ingo Molnar wrote: > * Avi Kivity <avi@redhat.com> wrote: > > >> Ingo Molnar wrote: >> >>>> Sure, go ahead and wrap them in some kind of "save and restore all >>>> registers" wrapping, but nothing fancier than that. It would just be >>>> overkill, and likely to break more than it fixes. >>>> >>>> >>> Yeah. I only brought up the virtualization thing as a >>> hypothetical: "if" corrupting the main OS ever became a >>> widespread problem. Then i made the argument that this is >>> unlikely to happen, because Windows will be affected by it just >>> as much. (while register state corruptions might go unnoticed >>> much more easily, just via the random call-environment clobbering >>> of registers by Windows itself.) >>> >>> The only case where i could see virtualization to be useful is >>> the low memory RAM corruption pattern that some people have >>> observed. >>> >> You could easily check that by checksumming pages (or actually >> copying them to high memory) before the call, and verifying after >> the call. >> > > Yes, we could do memory checks, and ... hey, we already do that: > > bb577f9: x86: add periodic corruption check > 5394f80: x86: check for and defend against BIOS memory corruption > > ... and i seem to be the one who implemented it! ;-) > > That check resulted in logs showing the BIOS corrupting Linux memory > across s2ram cycles or HDMI plug/unplug events on certain boxes (are > Hollywood rootkits in the BIOS now?), and resulted in some > head-scratching but not much more. >
Then there's definitely no point in putting it into a container, is there? I mean, we could track down the exact instruction which caused the corruption, but how would it help us?
>> I don't think the effort is worth the benefit in this case, but >> there actually is an interesting use case for this. SMM is known >> to be harmful to deterministic replay games and to real time >> response. If we can virtualize SMM, we can increase the range of >> hardware on which the real time kernel is able to deliver real >> time guarantees. >> > > Hey, i do have a real sweet spot for deterministic execution - but > SMM, while not problem-free (like most of firmware), also has a very > real role in not letting various hardware melt. So SMM should be > thought of as a flexible extended arm of hardware - not some sw bit. > > So i think that the memory of that SMM virtualization chapter you've > almost read should be quickly erased from your mind. (Via forceful > means if prompt corrective self-action is not forthcoming.) >
I'll keep my remaining neurons, thanks.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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