On Tue, Jan 05, 2010 at 04:12:42PM +0200, Gleb Natapov wrote: > KVM virtualizes guest memory by means of shadow pages or HW assistance > like NPT/EPT. Not all memory used by a guest is mapped into the guest > address space or even present in a host memory at any given time. > When vcpu tries to access memory page that is not mapped into the guest > address space KVM is notified about it. KVM maps the page into the guest > address space and resumes vcpu execution. If the page is swapped out > from host memory vcpu execution is suspended till the page is not swapped > into the memory again. This is inefficient since vcpu can do other work > (run other task or serve interrupts) while page gets swapped in. > > To overcome this inefficiency this patch series implements "asynchronous > page fault" for paravirtualized KVM guests. If a page that vcpu is > trying to access is swapped out KVM sends an async PF to the vcpu > and continues vcpu execution. Requested page is swapped in by another > thread in parallel. When vcpu gets async PF it puts faulted task to > sleep until "wake up" interrupt is delivered. When the page is brought > to the host memory KVM sends "wake up" interrupt and the guest's task > resumes execution. Some high level comments: - cr2 used as token: better use the shared region? what if: async pf queued guest triple faults without a vmexit inject async-pf-done with token in cr2 Also, in such scenario, can't you potentially corrupt guest memory after the triple fault by writing to the previously registered shared region address? - The token can overflow relatively easy. Use u64? - Does it really inject interrupts for non-pv guests while waiting for swapin? Can't see that. Wish it was more geared towards fv. - Please share some perf numbers. - Limit the number of queued async pf's per guest ? - Unify gfn_to_pfn / gfn_to_pfn_async code in the pf handlers (easier to review). -- 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
