Re: [RFCv2 11/16] KVM: Protected memory extension

[Peter Zijlstra]

On Tue, Oct 20, 2020 at 09:18:54AM +0300, Kirill A. Shutemov wrote:
> +int __kvm_protect_memory(unsigned long start, unsigned long end, bool protect)
> +{
> +	struct mm_struct *mm = current->mm;
> +	struct vm_area_struct *vma, *prev;
> +	int ret;
> +
> +	if (mmap_write_lock_killable(mm))
> +		return -EINTR;
> +
> +	ret = -ENOMEM;
> +	vma = find_vma(current->mm, start);
> +	if (!vma)
> +		goto out;
> +
> +	ret = -EINVAL;
> +	if (vma->vm_start > start)
> +		goto out;
> +
> +	if (start > vma->vm_start)
> +		prev = vma;
> +	else
> +		prev = vma->vm_prev;
> +
> +	ret = 0;
> +	while (true) {
> +		unsigned long newflags, tmp;
> +
> +		tmp = vma->vm_end;
> +		if (tmp > end)
> +			tmp = end;
> +
> +		newflags = vma->vm_flags;
> +		if (protect)
> +			newflags |= VM_KVM_PROTECTED;
> +		else
> +			newflags &= ~VM_KVM_PROTECTED;
> +
> +		/* The VMA has been handled as part of other memslot */
> +		if (newflags == vma->vm_flags)
> +			goto next;
> +
> +		ret = mprotect_fixup(vma, &prev, start, tmp, newflags);
> +		if (ret)
> +			goto out;
> +
> +next:
> +		start = tmp;
> +		if (start < prev->vm_end)
> +			start = prev->vm_end;
> +
> +		if (start >= end)
> +			goto out;
> +
> +		vma = prev->vm_next;
> +		if (!vma || vma->vm_start != start) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +	}
> +out:
> +	mmap_write_unlock(mm);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(__kvm_protect_memory);

Since migration will be disabled after this; should the above not (at
the very least) force compaction before proceeding to lock the pages in?