[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Woes of NMIs and MCEs, and possibly how to fix
>>> On 03.12.12 at 12:45, Mats Petersson <mats.petersson@xxxxxxxxxx> wrote: > On 03/12/12 11:24, George Dunlap wrote: >> On Fri, Nov 30, 2012 at 5:34 PM, Andrew Cooper >> <andrew.cooper3@xxxxxxxxxx <mailto:andrew.cooper3@xxxxxxxxxx>> wrote: >> >> 3) SMM mode executing an iret will re-enable NMIs. There is >> nothing we >> can do to prevent this, and as an SMI can interrupt NMIs and MCEs, no >> way to predict if/when it may happen. The best we can do is >> accept that >> it might happen, and try to deal with the after effects. >> >> >> Did you actually mean IRET, or did you mean RSM? Does it make a >> difference? > > If, for some obscure reason, the SMM code decides, for example, to run > code like "int 0x21", where the int 0x21 handler ends with the rather > predictable IRET to return to the caller, then you would indeed "unlock" > the NMI blocking that happens from the NMI being taken by the processor. > NMI will still not interrupt the SMM code, but it WILL interrupt the > code that was running before SMI was taken - which could be an NMI > handler, that doesn't expect another NMI. > > RSM doesn't, in and of itself [unless "messing" with the saved state] > alter the NMI state in other ways than "restore to previous value". And isn't it this "restore to previous value" that makes this a non-issue - after RSM, NMI-s would again be masked. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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