On 07/27/2011 07:08 PM, Avi Kivity wrote: > On 07/27/2011 01:20 PM, Xiao Guangrong wrote: >> >> } >> > >> > I think this is a little dangerous. A guest kernel may be instantiating >> > multiple gptes on a page fault, but guest userspace hits only one of them >> > (the one which caused the page fault) - I think Windows does this, but I'm >> > not sure. >> > >> >> I think this case is not bad: if the guest kernel need to write multiple >> gptes (>=3), >> it will cause many page fault, we do better zap the shadow page and let it >> become writable as >> soon as possible. >> (And, we have pte-fetch, it can quickly establish the mapping for a new >> shadow page) > > Actually, what should save us is unsync pages. Why are we hitting this path > at all? >
Avi, The shadow page can not became unsync if it has other sp that sp.gfn = gfn && sp.role.level != 1, for example: - if the gfn is not only used for the last page structure(PTE page) or - gfn was used for upper page structure before but we do not zap the old shadow pages So, if this gfn is written, #PF is generated, we hope that these sp can be zapped earlier, the later #PF can detect this gfn is not have shadow pages, and the mapping can became writable. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
