Re: [RFC v2 PATCH 07/13] KVM: Handle page fault for fd based memslot

[Chao Peng]

On Sat, Nov 20, 2021 at 09:55:29AM +0800, Yao Yuan wrote:
> On Fri, Nov 19, 2021 at 09:47:33PM +0800, Chao Peng wrote:
> > Current code assume the private memory is persistent and KVM can check
> > with backing store to see if private memory exists at the same address
> > by calling get_pfn(alloc=false).
> >
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c | 75 ++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 73 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 40377901598b..cd5d1f923694 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3277,6 +3277,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> >     if (max_level == PG_LEVEL_4K)
> >             return PG_LEVEL_4K;
> >
> > +   if (memslot_is_memfd(slot))
> > +           return max_level;
> > +
> >     host_level = host_pfn_mapping_level(kvm, gfn, pfn, slot);
> >     return min(host_level, max_level);
> >  }
> > @@ -4555,6 +4558,65 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu 
> > *vcpu, gpa_t cr2_or_gpa,
> >                               kvm_vcpu_gfn_to_hva(vcpu, gfn), &arch);
> >  }
> >
> > +static bool kvm_faultin_pfn_memfd(struct kvm_vcpu *vcpu,
> > +                             struct kvm_page_fault *fault, int *r)
> > +{  int order;
> > +   kvm_pfn_t pfn;
> > +   struct kvm_memory_slot *slot = fault->slot;
> > +   bool priv_gfn = kvm_vcpu_is_private_gfn(vcpu, fault->addr >> 
> > PAGE_SHIFT);
> > +   bool priv_slot_exists = memslot_has_private(slot);
> > +   bool priv_gfn_exists = false;
> > +   int mem_convert_type;
> > +
> > +   if (priv_gfn && !priv_slot_exists) {
> > +           *r = RET_PF_INVALID;
> > +           return true;
> > +   }
> > +
> > +   if (priv_slot_exists) {
> > +           pfn = slot->memfd_ops->get_pfn(slot, slot->priv_file,
> > +                                          fault->gfn, false, &order);
> > +           if (pfn >= 0)
> > +                   priv_gfn_exists = true;
> 
> Need "fault->pfn = pfn" here if actual pfn is returned in
> get_pfn(alloc=false) case for private page case.
> 
> > +   }
> > +
> > +   if (priv_gfn && !priv_gfn_exists) {
> > +           mem_convert_type = KVM_EXIT_MEM_MAP_PRIVATE;
> > +           goto out_convert;
> > +   }
> > +
> > +   if (!priv_gfn && priv_gfn_exists) {
> > +           slot->memfd_ops->put_pfn(pfn);
> > +           mem_convert_type = KVM_EXIT_MEM_MAP_SHARED;
> > +           goto out_convert;
> > +   }
> > +
> > +   if (!priv_gfn) {
> > +           pfn = slot->memfd_ops->get_pfn(slot, slot->file,
> > +                                          fault->gfn, true, &order);
> 
> Need "fault->pfn = pfn" here, because he pfn for
> share page is getted here only.
> 
> > +           if (fault->pfn < 0) {
> > +                   *r = RET_PF_INVALID;
> > +                   return true;
> > +           }
> > +   }

Right, I actually have "fault->pfn = pfn" here but accidentally deleted
in a code factoring.

Chao
> > +
> > +   if (slot->flags & KVM_MEM_READONLY)
> > +           fault->map_writable = false;
> > +   if (order == 0)
> > +           fault->max_level = PG_LEVEL_4K;
> > +
> > +   return false;
> > +
> > +out_convert:
> > +   vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
> > +   vcpu->run->mem.type = mem_convert_type;
> > +   vcpu->run->mem.u.map.gpa = fault->gfn << PAGE_SHIFT;
> > +   vcpu->run->mem.u.map.size = PAGE_SIZE;
> > +   fault->pfn = -1;
> > +   *r = -1;
> > +   return true;
> > +}
> > +
> >  static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault 
> > *fault, int *r)
> >  {
> >     struct kvm_memory_slot *slot = fault->slot;
> > @@ -4596,6 +4658,9 @@ static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, 
> > struct kvm_page_fault *fault,
> >             }
> >     }
> >
> > +   if (memslot_is_memfd(slot))
> > +           return kvm_faultin_pfn_memfd(vcpu, fault, r);
> > +
> >     async = false;
> >     fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
> >                                       fault->write, &fault->map_writable,
> > @@ -4660,7 +4725,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, 
> > struct kvm_page_fault *fault
> >     else
> >             write_lock(&vcpu->kvm->mmu_lock);
> >
> > -   if (fault->slot && mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, 
> > fault->hva))
> > +   if (fault->slot && !memslot_is_memfd(fault->slot) &&
> > +                   mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, fault->hva))
> >             goto out_unlock;
> >     r = make_mmu_pages_available(vcpu);
> >     if (r)
> > @@ -4676,7 +4742,12 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, 
> > struct kvm_page_fault *fault
> >             read_unlock(&vcpu->kvm->mmu_lock);
> >     else
> >             write_unlock(&vcpu->kvm->mmu_lock);
> > -   kvm_release_pfn_clean(fault->pfn);
> > +
> > +   if (memslot_is_memfd(fault->slot))
> > +           fault->slot->memfd_ops->put_pfn(fault->pfn);
> > +   else
> > +           kvm_release_pfn_clean(fault->pfn);
> > +
> >     return r;
> >  }
> >
> > --
> > 2.17.1
> >