linux-kernel - Re: [PATCH v4 18/66] xen: Use vma_lookup() in privcmd_ioctl

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Message-ID: <705ac4ab-34fb-e60f-aceb-d46e1913a28e@suse.cz>
Date:   Wed, 12 Jan 2022 17:01:04 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 18/66] xen: Use vma_lookup() in privcmd_ioctl_mmap()

On 12/1/21 15:29, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> 
> vma_lookup() walks the VMA tree for a specific value, find_vma() will
> search the tree after walking to a specific value.  It is more efficient
> to only walk to the requested value as this case requires the address to
> equal the vm_start.

By that you mean the privcmd_ioctl_mmap() code checks msg->va !=
vma->vm_start and thus we know it's never interested the next vma, that
find_vma() can return if no vma covers the address?

> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  drivers/xen/privcmd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 3369734108af..ad17166b0ef6 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -282,7 +282,7 @@ static long privcmd_ioctl_mmap(struct file *file, void __user *udata)
>  						     struct page, lru);
>  		struct privcmd_mmap_entry *msg = page_address(page);
>  
> -		vma = find_vma(mm, msg->va);
> +		vma = vma_lookup(mm, msg->va);
>  		rc = -EINVAL;
>  
>  		if (!vma || (msg->va != vma->vm_start) || vma->vm_private_data)