On 07/03/2013 04:39 PM, Xiao Guangrong wrote: > On 07/03/2013 04:28 PM, Paolo Bonzini wrote: >> Il 03/07/2013 10:18, Takuya Yoshikawa ha scritto: >>> Since kvm_arch_prepare_memory_region() is called right after installing >>> the slot marked invalid, wraparound checking should be there to avoid >>> zapping mmio sptes when mmio generation is still MMIO_MAX_GEN - 1. >>> >>> Signed-off-by: Takuya Yoshikawa <[email protected]> >>> --- >>> This seems to be the simplest solution for fixing the off-by-one issue >>> we discussed before. >>> >>> arch/x86/kvm/mmu.c | 5 +---- >>> arch/x86/kvm/x86.c | 7 +++++++ >>> 2 files changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index 0d094da..bf7af1e 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -4383,11 +4383,8 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >>> /* >>> * The very rare case: if the generation-number is round, >>> * zap all shadow pages. >>> - * >>> - * The max value is MMIO_MAX_GEN - 1 since it is not called >>> - * when mark memslot invalid. >>> */ >>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >>> + if (unlikely(kvm_current_mmio_generation(kvm) >= MMIO_MAX_GEN)) { >>> printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for >>> mmio generation wraparound\n"); >>> kvm_mmu_invalidate_zap_all_pages(kvm); >>> } >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index 7d71c0f..9ddd4ff 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -7046,6 +7046,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >>> memslot->userspace_addr = userspace_addr; >>> } >>> >>> + /* >>> + * In these cases, slots->generation has been increased for marking the >>> + * slot invalid, so we need wraparound checking here. >>> + */ >>> + if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) >>> + kvm_mmu_invalidate_mmio_sptes(kvm); >>> + >>> return 0; >>> } >>> >>> >> >> Applied, thanks. > > Please wait a while. I can not understand it very clearly. > > This conditional check will cause caching a overflow value into mmio spte. > The simple case is that kvm adds new slots for many times, the mmio-gen is > easily > more than MMIO_MAX_GEN. >
Actually, the double zapping can be avoided by moving kvm_mmu_invalidate_mmio_sptes to the end of install_new_memslots(). -- 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
