linux-kernel - Re: [PATCH v6 17/17] RFC: mm: add mmu_notifier argument to follow

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Date:   Fri, 20 Nov 2020 14:30:29 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-media@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v6 17/17] RFC: mm: add mmu_notifier argument to follow_pfn

On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
>   * Return: zero and the pfn at @pfn on success, -ve otherwise.
>   */
>  int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> -	unsigned long *pfn)
> +	unsigned long *pfn, struct mmu_notifier *subscription)
>  {
> -	int ret = -EINVAL;
> -	spinlock_t *ptl;
> -	pte_t *ptep;
> +	if (WARN_ON(!subscription->mm))
> +		return -EINVAL;
>  
> +	if (WARN_ON(subscription->mm != vma->vm_mm))
> +		return -EINVAL;

These two things are redundant right? vma->vm_mm != NULL?

BTW, why do we even have this for nommu? If the only caller is kvm,
can you even compile kvm on nommu??

Jason