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Date:   Tue, 20 Oct 2020 09:17:01 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Rientjes <rientjes@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Will Drewry <wad@chromium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
        "Kleen, Andi" <andi.kleen@intel.com>,
        Liran Alon <liran.alon@oracle.com>,
        Mike Rapoport <rppt@kernel.org>, x86@kernel.org,
        kvm@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFCv2 11/16] KVM: Protected memory extension
Message-ID: <20201020071701.GV2611@hirez.programming.kicks-ass.net>
References: <20201020061859.18385-1-kirill.shutemov@linux.intel.com>
 <20201020061859.18385-12-kirill.shutemov@linux.intel.com>
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In-Reply-To: <20201020061859.18385-12-kirill.shutemov@linux.intel.com>
Precedence: bulk

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?