linux-kernel - Re: [PATCH v2 16/16] kcov: update kcov to use mmap

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Message-ID: <20250915124801.GG1024672@nvidia.com>
Date: Mon, 15 Sep 2025 09:48:01 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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Subject: Re: [PATCH v2 16/16] kcov: update kcov to use mmap_prepare

On Mon, Sep 15, 2025 at 01:43:50PM +0100, Lorenzo Stoakes wrote:
> > > +	if (kcov->area == NULL || desc->pgoff != 0 ||
> > > +	    vma_desc_size(desc) != size) {
> >
> > IMHO these range checks should be cleaned up into a helper:
> >
> > /* Returns true if the VMA falls within starting_pgoff to
> >      starting_pgoff + ROUND_DOWN(length_bytes, PAGE_SIZE))
> >    Is careful to avoid any arithmetic overflow.
> >  */
> 
> Right, but I can't refactor every driver I touch, it's not really tractable. I'd
> like to get this change done before I retire :)

I don't think it is a big deal, and these helpers should be part of
the new api. You are reading and touching anyhow.

> > If anything the action should be called mmap_action_vmalloc_user() to
> > match how the memory was allocated instead of open coding something.
> 
> Again we're getting into the same issue - my workload doesn't really permit
> me to refactor every user of .mmap beyond converting sensibly to the new
> scheme.

If you are adding this explicit action concept then it should be a
sane set of actions. Using a mixed map action to insert a vmalloc_user
is not a reasonable thing to do.

Jason