Re: [PATCH 09/39] drivers/usb/mon: update to use mmap_prepare + map kernel pages

[sashiko-bot@kernel.org]

> Replace the deprecated .mmap hook with its replacement .mmap_prepare. As
> part of this change, additionally take the approach of mapping pages upon
> mmap rather than providing a fault handler.
> 
> The page span cannot be mutated when an mmap mapping is in place, so this
> is safe to do in advance (the MON_IOCT_RING_SIZE ioctl operation exits
> -EBUSY if it's attempted, gated by the rp->mmap_active reference count).
> 
> Utilise the newly introduced mmap_action_map_discontig_kernel_pages() to do
> this, which allows for iteration over pages in mon_bin_discontig_get().
> 
> mon_bin_discontig_init() increments the rp->mmap_active reference count to
> stabilise page spans. Should an error arise the core unmaps the VMA and
> mon_bin_vma_close() drops the reference again.
> 
> [ ... ]
> One behavioural difference: pages are no longer faulted in on demand, so a
> page discarded with MADV_DONTNEED is not repopulated and a subsequent
> access raises SIGBUS, as with other pre-populated kernel mappings.
> 
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260908-b4-mmap-prepare-vma-flag-sanify-v1-0-dacf19cce22b@kernel.org?part=9