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

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Message-ID: <c548e94d-5a06-464d-9076-b4a5d2e750dd@lucifer.local>
Date: Mon, 8 Sep 2025 14:47:26 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>,
        Guo Ren <guoren@...nel.org>,
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Subject: Re: [PATCH 16/16] kcov: update kcov to use mmap_prepare,
 mmap_complete

On Mon, Sep 08, 2025 at 10:30:13AM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 08, 2025 at 12:10:47PM +0100, Lorenzo Stoakes wrote:
> > Now we have the capacity to set up the VMA in f_op->mmap_prepare and then
> > later, once the VMA is established, insert a mixed mapping in
> > f_op->mmap_complete, do so for kcov.
> >
> > We utilise the context desc->mmap_context field to pass context between
> > mmap_prepare and mmap_complete to conveniently provide the size over which
> > the mapping is performed.
>
> Why?
>
> +	    vma_desc_size(desc) != size) {
> +  		res = -EINVAL;
>
> Just call some vma_size()?

Ah yeah we can do you're right, as we assert vma_desc_size() == size, will fix
that thanks!

There is no vma_size() though, which is weird to me. There is vma_pages() <<
PAGE_SHIFT though...

Maybe one to add!

>
> Jason

Cheers, Lorenzo