On Wed, Mar 15, 2023 at 10:12 PM Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> wrote: > > On martedì 14 marzo 2023 04:56:08 CET Jason Wang wrote: > > On Thu, Mar 2, 2023 at 7:34 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> > wrote: > > > kmap_atomic() is deprecated in favor of kmap_local_page(). > > > > It's better to mention the commit or code that introduces this. > > > > > With kmap_local_page() the mappings are per thread, CPU local, can take > > > page-faults, and can be called from any context (including interrupts). > > > Furthermore, the tasks can be preempted and, when they are scheduled to > > > run again, the kernel virtual addresses are restored and still valid. > > > > > > kmap_atomic() is implemented like a kmap_local_page() which also disables > > > page-faults and preemption (the latter only for !PREEMPT_RT kernels, > > > otherwise it only disables migration). > > > > > > The code within the mappings/un-mappings in getu16_iotlb() and > > > putu16_iotlb() don't depend on the above-mentioned side effects of > > > kmap_atomic(), > > > > Note we used to use spinlock to protect simulators (at least until > > patch 7, so we probably need to re-order the patches at least) so I > > think this is only valid when: > > > > The vringh IOTLB helpers are not used in atomic context (e.g spinlock, > > interrupts). > > I'm probably missing some context but it looks that you are saying that > kmap_local_page() is not suited for any use in atomic context (you are > mentioning spinlocks). > > The commit message (that I know pretty well since it's the exact copy, word by > word, of my boiler plate commits) I hope it's not a problem for you, should I mention it somehow? I searched for the last commits that made a similar change and found yours that explained it perfectly ;-) Do I need to rephrase? > explains that kmap_local_page() is perfectly > usable in atomic context (including interrupts). > > I don't know this code, however I am not able to see why these vringh IOTLB > helpers cannot work if used under spinlocks. Can you please elaborate a little > more? > > > If yes, should we document this? (Or should we introduce a boolean to > > say whether an IOTLB variant can be used in an atomic context)? > > Again, you'll have no problems from the use of kmap_local_page() and so you > don't need any boolean to tell whether or not the code is running in atomic > context. > > Please take a look at the Highmem documentation which has been recently > reworked and extended by me: https://docs.kernel.org/mm/highmem.html > > Anyway, I have been ATK 12 or 13 hours in a row. So I'm probably missing the > whole picture. Thanks for your useful info! Stefano _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
