On 03/18/2013 09:19 PM, Gleb Natapov wrote: > On Mon, Mar 18, 2013 at 09:09:43PM +0800, Xiao Guangrong wrote: >> On 03/18/2013 08:46 PM, Gleb Natapov wrote: >>> On Mon, Mar 18, 2013 at 08:29:29PM +0800, Xiao Guangrong wrote: >>>> On 03/18/2013 05:13 PM, Gleb Natapov wrote: >>>>> On Mon, Mar 18, 2013 at 04:08:50PM +0800, Xiao Guangrong wrote: >>>>>> On 03/17/2013 11:02 PM, Gleb Natapov wrote: >>>>>>> On Fri, Mar 15, 2013 at 11:29:53PM +0800, Xiao Guangrong wrote: >>>>>>>> This patch tries to introduce a very simple and scale way to invalid all >>>>>>>> mmio sptes - it need not walk any shadow pages and hold mmu-lock >>>>>>>> >>>>>>>> KVM maintains a global mmio invalid generation-number which is stored in >>>>>>>> kvm->arch.mmio_invalid_gen and every mmio spte stores the current global >>>>>>>> generation-number into his available bits when it is created >>>>>>>> >>>>>>>> When KVM need zap all mmio sptes, it just simply increase the global >>>>>>>> generation-number. When guests do mmio access, KVM intercepts a MMIO #PF >>>>>>>> then it walks the shadow page table and get the mmio spte. If the >>>>>>>> generation-number on the spte does not equal the global generation-number, >>>>>>>> it will go to the normal #PF handler to update the mmio spte >>>>>>>> >>>>>>>> Since 19 bits are used to store generation-number on mmio spte, the >>>>>>>> generation-number can be round after 33554432 times. It is large enough >>>>>>>> for nearly all most cases, but making the code be more strong, we zap all >>>>>>>> shadow pages when the number is round >>>>>>>> >>>>>>> Very nice idea, but why drop Takuya patches instead of using >>>>>>> kvm_mmu_zap_mmio_sptes() when generation number overflows. >>>>>> >>>>>> I am not sure whether it is still needed. Requesting to zap all mmio sptes for >>>>>> more than 500000 times is really really rare, it nearly does not happen. >>>>>> (By the way, 33554432 is wrong in the changelog, i just copy that for my origin >>>>>> implantation.) And, after my patch optimizing zapping all shadow pages, >>>>>> zap-all-sps should not be a problem anymore since it does not take too much lock >>>>>> time. >>>>>> >>>>>> Your idea? >>>>>> >>>>> I expect 500000 to become less since I already had plans to store some >>>> >>>> Interesting, just curious, what are the plans? ;) >>>> >>> Currently we uses pio to signal that work is pending to virtio devices. The >>> requirement is that signaling should be fast and PIO is fast since there >>> is not need to emulate instruction. PCIE though is not really designed >>> with PIO in mind, so we will have to use MMIO to do signaling. To avoid >>> instruction emulation I thought about making guest access these devices using >>> predefined variety of MOV instruction so that emulation can be skipped. >>> The idea is to mark mmio spte to know that emulation is not needed. >> >> How to know page-fault is caused by the predefined instruction? >> > Only predefined phys address rages will be accessed that way. If page > fault is in a range we assume the knows instruction is used. That means the access can be identified by the gfn, why need cache other things into mmio spte? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
