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

Yao Yuan
2021-11-20T01:55:39Z

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;
> + }
> + }
> +
> + 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
>