* H. Peter Anvin (hpa@xxxxxxxxx) wrote: > Linus Torvalds wrote: > > > > On Mon, 15 Jun 2009, Ingo Molnar wrote: > >> A simple cr2 corruption would explain all those cc1 SIGSEGVs and > >> other user-space crashes i saw, with sufficiently intense sampling - > >> easily. > > > > Note that we could work around the %cr2 issue, since any corruption is > > always nicely "nested" (ie there are never any SMP issues with async > > writes to the register). > > > > So what we _could_ do is to have a magic value for %cr2, along with a "NMI > > sequence count", and if we see that value, we just return (without doing > > anything) from the page fault handler. > > > > Wouldn't it be simpler to just require the NMI handler to save and > restore %cr2 around any potentially faulting references? > > -hpa If we require that around the whole NMI handler execution, then we get all vmalloc + module text code references handled for free. This would be a nice-to-have.a And given nmi-handler is not such a frequent code path, we should not care that much about the performance hit of saving/restoring the cr2 register at each nmi entry/exit. Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|