On Wed, Sep 28, 2022, Zhao Liu wrote: > From: Zhao Liu <zhao1.liu@xxxxxxxxx> > > The use of kmap_atomic() is being deprecated in favor of > kmap_local_page()[1]. > > The main difference between kmap_atomic() and kmap_local_page() is the > latter allows pagefaults and preemption. > > There're 2 reasons we can use kmap_local_page() here: > 1. SEV is 64-bit only and kmap_locla_page() doesn't disable migration in > this case, but here the function clflush_cache_range() uses CLFLUSHOPT > instruction to flush, and on x86 CLFLUSHOPT is not CPU-local and flushes > the page out of the entire cache hierarchy on all CPUs (APM volume 3, > chapter 3, CLFLUSHOPT). So there's no need to disable preemption to ensure > CPU-local. > 2. clflush_cache_range() doesn't need to disable pagefault and the mapping > is still valid even if sleeps. This is also true for sched out/in when > preempted. > > In addition, though kmap_local_page() is a thin wrapper around > page_address() on 64-bit, kmap_local_page() should still be used here in > preference to page_address() since page_address() isn't suitable to be used > in a generic function (like sev_clflush_pages()) where the page passed in > is not easy to determine the source of allocation. Keeping the kmap* API in > place means it can be used for things other than highmem mappings[2]. > > Therefore, sev_clflush_pages() is a function that should use > kmap_local_page() in place of kmap_atomic(). > > Convert the calls of kmap_atomic() / kunmap_atomic() to kmap_local_page() / > kunmap_local(). > > [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@xxxxxxxxx > [2]: https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@xxxxxxxxx/ > > Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx> > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Suggested-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx> > --- Merged to kvm/queue, thanks! https://lore.kernel.org/all/Y4lHxds8pvBhxXFX@xxxxxxxxxx
