Re: [PATCH v3 7/8] ARM: KVM: Handle guest faults in KVM

[Avi Kivity <avi@redhat.com>]

On 06/03/2011 06:04 PM, Christoffer Dall wrote:
> Handles the guest faults in KVM by mapping in corresponding user pages
> in the 2nd stage page tables.
>
>
>
> +static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> +			  gfn_t gfn, struct kvm_memory_slot *memslot)
> +{
> +	pfn_t pfn;
> +	pgd_t *pgd;
> +	pmd_t *pmd;
> +	pte_t *pte, new_pte;
> +
> +	pfn = gfn_to_pfn(vcpu->kvm, gfn);
> +
> +	if (is_error_pfn(pfn)) {
> +		kvm_err(-EFAULT, "Guest gfn %u (0x%08lx) does not have "
> +				"corresponding host mapping",
> +				gfn, gfn<<  PAGE_SHIFT);
> +		return -EFAULT;
> +	}
> +
> +	/* Create 2nd stage page table mapping - Level 1 */
> +	pgd = vcpu->kvm->arch.pgd + pgd_index(fault_ipa);
> +	if (pgd_none(*pgd)) {
> +		pmd = pmd_alloc_one(NULL, fault_ipa);
> +		if (!pmd) {
> +			kvm_err(-ENOMEM, "Cannot allocate 2nd stage pmd");
> +			return -ENOMEM;
> +		}
> +		pgd_populate(NULL, pgd, pmd);
> +		pmd += pmd_index(fault_ipa);
> +	} else
> +		pmd = pmd_offset(pgd, fault_ipa);
> +
> +	/* Create 2nd stage page table mapping - Level 2 */
> +	if (pmd_none(*pmd)) {
> +		pte = pte_alloc_one_kernel(NULL, fault_ipa);
> +		if (!pte) {
> +			kvm_err(-ENOMEM, "Cannot allocate 2nd stage pte");
> +			return -ENOMEM;
> +		}
> +		pmd_populate_kernel(NULL, pmd, pte);
> +		pte += pte_index(fault_ipa);
> +	} else
> +		pte = pte_offset_kernel(pmd, fault_ipa);
> +
> +	/* Create 2nd stage page table mapping - Level 3 */
> +	new_pte = pfn_pte(pfn, PAGE_KVM_GUEST);
> +	set_pte_ext(pte, new_pte, 0);
> +
> +	return 0;
> +}
> +
> +#define HSR_ABT_FS	(0x3f)
> +#define HPFAR_MASK	(~0xf)
>   int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>   {
> +	unsigned long hsr_ec;
> +	unsigned long fault_status;
> +	phys_addr_t fault_ipa;
> +	struct kvm_memory_slot *memslot = NULL;
> +	bool is_iabt;
> +	gfn_t gfn;
> +
> +	hsr_ec = vcpu->arch.hsr>>  HSR_EC_SHIFT;
> +	is_iabt = (hsr_ec == HSR_EC_IABT);
> +
> +	/* Check that the second stage fault is a translation fault */
> +	fault_status = vcpu->arch.hsr&  HSR_ABT_FS;
> +	if ((fault_status&  0x3c) != 0x4) {
> +		kvm_err(-EFAULT, "Unsupported fault status: %x",
> +				fault_status&  0x3c);
> +		return -EFAULT;
> +	}
> +
> +	fault_ipa = ((phys_addr_t)vcpu->arch.hpfar&  HPFAR_MASK)<<  8;
> +
> +	gfn = fault_ipa>>  PAGE_SHIFT;
> +	if (!kvm_is_visible_gfn(vcpu->kvm, gfn))
> +		goto io_mem_abort;
> +
> +	memslot = gfn_to_memslot(vcpu->kvm, gfn);
> +	if (memslot->user_alloc)
> +		return user_mem_abort(vcpu, fault_ipa, gfn, memslot);

Non-user_alloc should not exist for ARM (and are not supported for x86 
these days, except for a few implementation internal slots).

> +
> +io_mem_abort:
> +	if (is_iabt) {
> +		kvm_err(-EFAULT, "Inst. abort on I/O address");
> +		return -EFAULT;
> +	}
> +
> +	kvm_msg("I/O address abort...");
>   	KVMARM_NOT_IMPLEMENTED();
>   	return -EINVAL;
>   }

Okay, this is about a zillion times simpler than x86.  Congratulations.

What are your thoughts about mmu notifier support?


-- 
error compiling committee.c: too many arguments to function