Messages in this thread | | | Date | Wed, 23 Nov 2016 15:05:21 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/mce: Include the PPIN in machine check records when it is available |
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On Wed, Nov 23, 2016 at 02:37:23PM +0100, Borislav Petkov wrote: > You can't reenable it: > > "LockOut (R/WO) > Set 1 to prevent further writes to MSR_PPIN_CTL. Writing 1 to > MSR_PPINCTL[bit 0] is permitted only if MSR_PPIN_CTL[bit 1] is > clear, Default is 0."
Well, almost.
"Enable_PPIN (R/W) If 1, enables MSR_PPIN to be accessible using RDMSR. Once set, attempt to write 1 to MSR_PPIN_CTL[bit 0] will cause #GP. If 0, an attempt to read MSR_PPIN will cause #GP. Default is 0."
Frankly, I don't get what the deal behind that locking out is. And it says that BIOS should provide an opt-in so that agent can read the PPIN and then that agent should *disable* it again by writing 01b to the CTL MSR.
But then the first paragraph above says that the write MSR_PPIN_CTL[0]=1b will #GP because MSR_PPIN_CTL[1] will be 1 for the agent to read out MSR_PPIN first.
I guess we need to write a 00b first to disable PPIN and then write 01b to lock it out.
So AFAIU, the steps will be:
* BIOS writes 10b * agent reads MSR_PPIN * agent writes 00b to disable MSR_PPIN * agent writes 01b because bit 1 is clear now and it won't #GP.
Meh...
-- Regards/Gruss, Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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