Subject: Re: [PATCH v1 3/4] KVM: PPC: Book3S HV: migrate remaining normal-GFNs to secure-GFNs in H_SVM_INIT_DONE

From: Bharata B Rao <[email-masked]>
Date: Mon, 1 Jun 2020 17:25:18 +0530

On Sat, May 30, 2020 at 07:27:50PM -0700, Ram Pai wrote:
> H_SVM_INIT_DONE incorrectly assumes that the Ultravisor has explicitly
> called H_SVM_PAGE_IN for all secure pages.

I don't think that is quite true. HV doesn't assume anything about
secure pages by itself.

> These GFNs continue to be
> normal GFNs associated with normal PFNs; when infact, these GFNs should
> have been secure GFNs associated with device PFNs.

Transition to secure state is driven by SVM/UV and HV just responds to
hcalls by issuing appropriate uvcalls. SVM/UV is in the best position to
determine the required pages that need to be moved into secure side.
HV just responds to it and tracks such pages as device private pages.

If SVM/UV doesn't get in all the pages to secure side by the time
of H_SVM_INIT_DONE, the remaining pages are just normal (shared or
otherwise) pages as far as HV is concerned.  Why should HV assume that
SVM/UV didn't ask for a few pages and hence push those pages during
H_SVM_INIT_DONE?

I think UV should drive the movement of pages into secure side both
of boot-time SVM memory and hot-plugged memory. HV does memslot
registration uvcall when new memory is plugged in, UV should explicitly
get the required pages in at that time instead of expecting HV to drive
the same.

> +static int uv_migrate_mem_slot(struct kvm *kvm,
> +		const struct kvm_memory_slot *memslot)
> +{
> +	unsigned long gfn = memslot->base_gfn;
> +	unsigned long end;
> +	bool downgrade = false;
> +	struct vm_area_struct *vma;
> +	int i, ret = 0;
> +	unsigned long start = gfn_to_hva(kvm, gfn);
> +
> +	if (kvm_is_error_hva(start))
> +		return H_STATE;
> +
> +	end = start + (memslot->npages << PAGE_SHIFT);
> +
> +	down_write(&kvm->mm->mmap_sem);
> +
> +	mutex_lock(&kvm->arch.uvmem_lock);
> +	vma = find_vma_intersection(kvm->mm, start, end);
> +	if (!vma || vma->vm_start > start || vma->vm_end < end) {
> +		ret = H_STATE;
> +		goto out_unlock;
> +	}
> +
> +	ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> +			  MADV_UNMERGEABLE, &vma->vm_flags);
> +	downgrade_write(&kvm->mm->mmap_sem);
> +	downgrade = true;
> +	if (ret) {
> +		ret = H_STATE;
> +		goto out_unlock;
> +	}
> +
> +	for (i = 0; i < memslot->npages; i++, ++gfn) {
> +		/* skip paged-in pages and shared pages */
> +		if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL) ||
> +			kvmppc_gfn_is_uvmem_shared(gfn, kvm))
> +			continue;
> +
> +		start = gfn_to_hva(kvm, gfn);
> +		end = start + (1UL << PAGE_SHIFT);
> +		ret = kvmppc_svm_migrate_page(vma, start, end,
> +			(gfn << PAGE_SHIFT), kvm, PAGE_SHIFT, false);
> +
> +		if (ret)
> +			goto out_unlock;
> +	}

Is there a guarantee that the vma you got for the start address remains
valid for all the addresses till end in a memslot? If not, you should
re-get the vma for the current address in each iteration I suppose.

Regards,
Bharata.