Re: KVM: MMU: handle invalid root_hpa at __direct_map

[Marcelo Tosatti <mtosatti@redhat.com>]

On Fri, Jan 17, 2014 at 01:17:21AM +0200, Rom Freiman wrote:
> Hi everybody,
> Marcelo, your suggestion above should work together with the same
> patch to __direct_mapping.
> 
> After running some test on different kernels, the !VALID_PAGE happens
> as following:
> 
> Linux localhost.localdomain 3.12.5-200.fc19.x86_64 #1 SMP Tue Dec 17
> 22:21:14 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux:
> INVALID PAGE kvm/arch/x86/kvm/paging_tmpl.h:FNAME(fetch):573: ffffffffffffffff
> 
> Linux localhost.localdomain
> 3.11.8-200.strato0002.fc19.strato.44671928e2e2.x86_64 #1 SMP Sun Jan 5
> 18:30:38 IST 2014 x86_64 x86_64 x86_64 GNU/Linux:
> INVALID PAGE arch/x86/kvm/mmu.c:__direct_map:2695: ffffffffffffffff
> 
> So u probably should add both patches to kvm.
> 
> Here is my complete patch for 3.11, if you like:
> 
> diff --git a/kvm/arch/x86/kvm/mmu.c b/kvm/arch/x86/kvm/mmu.c
> index 9e9285a..c38e480 100644
> --- a/kvm/arch/x86/kvm/mmu.c
> +++ b/kvm/arch/x86/kvm/mmu.c
> @@ -2691,6 +2691,11 @@ static int __direct_map(struct kvm_vcpu *vcpu,
> gpa_t v, int write,
>         int emulate = 0;
>         gfn_t pseudo_gfn;
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +                return 0;
> +       }
> +
>         for_each_shadow_entry(vcpu, (u64)gfn << PAGE_SHIFT, iterator) {
>                 if (iterator.level == level) {
>                         mmu_set_spte(vcpu, iterator.sptep, ACC_ALL,
> @@ -2861,6 +2866,11 @@ static bool fast_page_fault(struct kvm_vcpu
> *vcpu, gva_t gva, int level,
>         bool ret = false;
>         u64 spte = 0ull;
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +               return false;
> +       }
> +
>         if (!page_fault_can_be_fast(vcpu, error_code))
>                 return false;
> 
> @@ -3255,6 +3265,11 @@ static u64
> walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr)
>         struct kvm_shadow_walk_iterator iterator;
>         u64 spte = 0ull;
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +               return spte;
> +       }
> +
>         walk_shadow_page_lockless_begin(vcpu);
>         for_each_shadow_entry_lockless(vcpu, addr, iterator, spte)
>                 if (!is_shadow_present_pte(spte))
> @@ -4525,6 +4540,11 @@ int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu
> *vcpu, u64 addr, u64 sptes[4])
>         u64 spte;
>         int nr_sptes = 0;
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +               return nr_sptes;
> +       }
> +
>         walk_shadow_page_lockless_begin(vcpu);
>         for_each_shadow_entry_lockless(vcpu, addr, iterator, spte) {
>                 sptes[iterator.level-1] = spte;
> 
> diff --git a/kvm/arch/x86/kvm/paging_tmpl.h b/kvm/arch/x86/kvm/paging_tmpl.h
> index 7769699..202a1fc 100644
> --- a/kvm/arch/x86/kvm/paging_tmpl.h
> +++ b/kvm/arch/x86/kvm/paging_tmpl.h
> @@ -423,6 +423,11 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>         if (FNAME(gpte_changed)(vcpu, gw, top_level))
>                 goto out_gpte_changed;
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +               goto out_gpte_changed;
> +       }
> +
>         for (shadow_walk_init(&it, vcpu, addr);
>              shadow_walk_okay(&it) && it.level > gw->level;
>              shadow_walk_next(&it)) {
> @@ -674,6 +679,12 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
>          */
>         mmu_topup_memory_caches(vcpu);
> 
> +       if (!VALID_PAGE(vcpu->arch.mmu.root_hpa)) {
> +               pgprintk(KERN_WARNING "invalid page access %s:%s:%d:
> %llx\n",  __FILE__, __func__, __LINE__, vcpu->arch.mmu.root_hpa);
> +               WARN_ON(1);
> +                return;
> +       }
> 
> 
> Another issue I'm struggling with is the next bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=1052861
> 
> The only thing i'm trying to over there is to run virt-v2v in nested
> environment. May be you have any idea?
> It's also related to memory pressure on L2. Of coarse L0 does not
> crash (using it with the above patch) but L2 is crushing during the
> conversion process.

No idea. I'd start from the double fault.

Tried tracing KVM exception injection in both L0 and L1 
and correlate (event injection by KVM) with the one you see?

http://www.linux-kvm.org/page/Tracing

http://www.linux-kvm.org/page/Perf_events#Tracing_events