Hi Fabio, On Wed, Nov 29, 2023 at 3:41 AM Fabio M. De Francesco <fabio.maria.de.francesco@xxxxxxxxxxxxxxx> wrote: > > > The kernel virtual addresses returned by these two API are > > > only valid in the context of the callers (i.e., they cannot be handed to > > > other threads). > > > > > > With kmap_local_page() the mappings are per thread and CPU local like > > > in kmap_atomic(); however, they can handle page-faults and can be called > > > from any context (including interrupts). The tasks that call > > > kmap_local_page() can be preempted and, when they are scheduled to run > > > again, the kernel virtual addresses are restored and are still valid. > > > > As far as I can tell, the kmap_atomic() is the same as > > kmap_local_page() with the following additional code before calling to > > "__kmap_local_page_prot(page, prot)", which is common between these > > two functions. > > > > if (IS_ENABLED(CONFIG_PREEMPT_RT)) > > migrate_disable(); > > else > > preempt_disable(); > > > > pagefault_disable(); > > > > This is what I tried to explain with that sentence. I think you overlooked it > :) I did read your description. It is not that I don't trust your description. I want to see how the code does what you describe at the source code level. In this case the related code is fairly easy to isolate. > > BTW, please have a look at the Highmem documentation. It has initially been > written by Peter Z. and I reworked and largely extended it authoring the > patches with my gmail address (6 - 7 different patches, if I remember > correctly). > > You will find there everything you may want to know about these API and how to > do conversions from the older to the newer. Will do, thanks for the pointer. Chris
