On 13/10/2017 23:48, Peng Hao wrote: > When poweroff L1 Guest with L2 guset on L1, it exists a path to > trigger a bad_page bug_on.
How easy it is to reproduce? CCing Junaid and Guangrong too. > !page_count(pfn_to_page(pfn)) Warning in mmu_spte_clear_track_bits will > appear before,then it may set A/D bit for the freed page and trigger a > bad_page bug_on. > > Signed-off-by: Peng Hao <[email protected]> > --- > arch/x86/kvm/mmu.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index eca30c1..398de96 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -711,12 +711,8 @@ static int mmu_spte_clear_track_bits(u64 *sptep) > > pfn = spte_to_pfn(old_spte); > > - /* > - * KVM does not hold the refcount of the page used by > - * kvm mmu, before reclaiming the page, we should > - * unmap it from mmu first. > - */ > - WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn))); > + if (!page_count(pfn_to_page(pfn))) > + return 1; If the page count is zero, KVM should not have accessed this page at all. The bug is elsewhere. :( Paolo > if (is_accessed_spte(old_spte)) > kvm_set_pfn_accessed(pfn); >
