linux-kernel - Re: [PATCH 2/4] KVM: arm64: Use find_vma

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Date:   Mon, 15 Mar 2021 08:52:38 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        will@...nel.org, alexandru.elisei@....com, shan.gavin@...il.com
Subject: Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

On Mon, 15 Mar 2021 04:18:42 +0000,
Gavin Shan <gshan@...hat.com> wrote:
> 
> find_vma_intersection() has been existing to search the intersected
> vma. This uses the function where it's applicable, to simplify the
> code.
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>  arch/arm64/kvm/mmu.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 84e70f953de6..286b603ed0d3 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>  	 *     +--------------------------------------------+
>  	 */
>  	do {
> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
> +		struct vm_area_struct *vma;
>  		hva_t vm_start, vm_end;
>  
> -		if (!vma || vma->vm_start >= reg_end)
> +		vma = find_vma_intersection(current->mm, hva, reg_end);

For context, here's the definition of find_vma_intersection():

<quote>
static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
{
	struct vm_area_struct * vma = find_vma(mm,start_addr);

	if (vma && end_addr <= vma->vm_start)
		vma = NULL;
	return vma;
}
</quote>

It seems that there is a boundary issue in either the old code or the
new one in the case where (reg_end == vma->start).

Which one is which?

	M.

-- 
Without deviation from the norm, progress is not possible.