On Tue, Jul 30, 2013 at 09:02:02PM +0800, Xiao Guangrong wrote: > Make sure we can see the writable spte before the dirt bitmap is visible > > We do this is for kvm_vm_ioctl_get_dirty_log() write-protects the spte based > on the dirty bitmap, we should ensure the writable spte can be found in rmap > before the dirty bitmap is visible. Otherwise, we cleared the dirty bitmap and > failed to write-protect the page > > Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> > --- > arch/x86/kvm/mmu.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) Can you explain why this is safe, with regard to the rule at edde99ce05290e50 ? "The rule is that all pages are either dirty in the current bitmap, or write-protected, which is violated here." Overall, please document what is the required order of operations for both set_spte and get_dirty_log and why this order is safe (right on top of the code). > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 35d4b50..0fe56ad 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -2486,12 +2486,12 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, > } > } > > - if (pte_access & ACC_WRITE_MASK) > - mark_page_dirty(vcpu->kvm, gfn); > - > set_pte: > if (mmu_spte_update(sptep, spte)) > kvm_flush_remote_tlbs(vcpu->kvm); Here, there is a modified guest page without dirty log bit set (think another vcpu writing to the page via this spte). > + > + if (pte_access & ACC_WRITE_MASK) > + mark_page_dirty(vcpu->kvm, gfn); > done: > return ret; > } > -- > 1.8.1.4 -- 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
