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

[Yao Yuan]

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@xxxxxxxxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
>  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
>