Re: [PATCH v2 bpf-next 04/20] mm: Expose vmap_pages_range() to the rest of the kernel.

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NAK.  Please

On Thu, Feb 08, 2024 at 08:05:52PM -0800, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
> 
> BPF would like to use the vmap API to implement a lazily-populated
> memory space which can be shared by multiple userspace threads.
> The vmap API is generally public and has functions to request and

What is "the vmap API"?

> For example, there is the public ioremap_page_range(), which is used
> to map device memory into addressable kernel space.

It's not really public.  It's a helper for the ioremap implementation
which really should not be arch specific to start with and are in
the process of beeing consolidatd into common code.

> The new BPF code needs the functionality of vmap_pages_range() in
> order to incrementally map privately managed arrays of pages into its
> vmap area. Indeed this function used to be public, but became private
> when usecases other than vmalloc happened to disappear.

Yes, for a freaking good reason.  The vmap area is not for general abuse
by random callers.  We have a few of those left, but we need to get rid
of that and not add more.





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