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

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Message-ID: <fdkqhtegozzwx3p4fqzkar7dfbzffn7xiz7ht365c3pe4x6hk3@zbfwoktrhci3>
Date: Wed, 17 Sep 2025 12:07:52 +0100
From: Pedro Falcato <pfalcato@...e.de>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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Subject: Re: [PATCH v3 06/13] mm: add remap_pfn_range_prepare(),
 remap_pfn_range_complete()

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?


> 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>

-- 
Pedro