linux-kernel - Re: [PATCH v3 06/13] mm: add remap_pfn_range_prepare(), remap_pfn_range

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Message-ID: <8ff73b67-ebe4-4407-905e-3fbc27bb5c2b@lucifer.local>
Date: Wed, 17 Sep 2025 12:16:46 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Pedro Falcato <pfalcato@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v3 06/13] mm: add remap_pfn_range_prepare(),
 remap_pfn_range_complete()

On Wed, Sep 17, 2025 at 12:07:52PM +0100, Pedro Falcato wrote:
> On Tue, Sep 16, 2025 at 03:11:52PM +0100, Lorenzo Stoakes wrote:
> > We need the ability to split PFN remap between updating the VMA and
> > performing the actual remap, in order to do away with the legacy
> > f_op->mmap hook.
> >
> > To do so, update the PFN remap code to provide shared logic, and also make
> > remap_pfn_range_notrack() static, as its one user, io_mapping_map_user()
> > was removed in commit 9a4f90e24661 ("mm: remove mm/io-mapping.c").
> >
> > Then, introduce remap_pfn_range_prepare(), which accepts VMA descriptor
> > and PFN parameters, and remap_pfn_range_complete() which accepts the same
> > parameters as remap_pfn_rangte().
>                 remap_pfn_range
>
> >
> > remap_pfn_range_prepare() will set the cow vma->vm_pgoff if necessary, so
> > it must be supplied with a correct PFN to do so.  If the caller must hold
> > locks to be able to do this, those locks should be held across the
> > operation, and mmap_abort() should be provided to revoke the lock should
> > an error arise.
> >
> > While we're here, also clean up the duplicated #ifdef
> > __HAVE_PFNMAP_TRACKING check and put into a single #ifdef/#else block.
> >
> > We would prefer to define these functions in mm/internal.h, however we
> > will do the same for io_remap*() and these have arch defines that require
> > access to the remap functions.
> >
>
> I'm confused. What's stopping us from declaring these new functions in
> internal.h? It's supposed to be used by core mm only anyway?

See reply to io_remap_pfn_range_*() patch :)

>
>
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> The changes themselves look OK to me, but I'm not super familiar with these
> bits anyway.
>
> Acked-by: Pedro Falcato <pfalcato@...e.de>

Thanks! :)

>
> --
> Pedro

Cheers, Lorenzo