On 5/16/22 23:28, Rolf Eike Beer wrote: > Am Montag, 16. Mai 2022, 17:14:47 CEST schrieb John David Anglin: >> Originally, I was convinced that we needed to use tmpalias flushes >> everwhere, for both user and kernel flushes. However, when I modified >> flush_kernel_dcache_page_addr, to use a tmpalias flush, my c8000 >> would crash quite early when booting. >> >> The PDC returns alias values of 0 for the icache and dcache. This >> indicates that either the alias boundary is greater than 16MB or >> equivalent aliasing doesn't work. I modified the tmpalias code to >> make it easy to try alternate boundaries. I tried boundaries up to >> 128MB but still kernel tmpalias flushes didn't work on c8000. >> >> This led me to conclude that tmpalias flushes don't work on PA8800 >> and PA8900 machines, and that we needed to flush directly using the >> virtual address of user and kernel pages. This is likely the major >> cause of instability on the c8000 and rp34xx machines. >> >> Flushing user pages requires doing a temporary context switch as we >> have to flush pages that don't belong to the current context. Further, >> we have to deal with pages that aren't present. If a page isn't >> present, the flush instructions fault on every line. >> >> Other code has been rearranged and simplified based on testing. For >> example, I introduced a flush_cache_dup_mm routine. flush_cache_mm >> and flush_cache_dup_mm differ in that flush_cache_mm calls >> purge_cache_pages and flush_cache_dup_mm calls flush_cache_pages. >> In some implementations, pdc is more efficient than fdc. Based on >> my testing, I don't believe there's any performance benefit on the >> c8000. >> >> V2: >> 1) Add flush_cache_page_check_pte routine. >> 2) Use it in copy_to_user_page and copy_from_user_page. >> 3) flush_anon_page moved to cache.c and updated. >> 4) Changed alias boundary to 64 MB for 64-bit kernels. Revised comment >> regarding alias boundary for PA8800/PA8900 processors. >> 5) Removed struct mm_struct * argument from flush_cache_pages. >> 6) Fixed thinko in flush_cache_range. It increased the number of pages >> flushed and slowed performance. >> 7) Removed sync changes from pacache.S. >> >> V3: >> 1) copy_to_user_page and copy_from_user_page moved to cache.c to >> improve inlining. >> 2) Replaced copy_user_page with copy_user_highpage. >> 3) Fixed cache threshold calculation on 32-bit kernels. >> 4) Don't warn on inequivalent private mappings in flush_dcache_page. >> 5) Return early from mm_total_size if size exceeds >> parisc_cache_flush_threshold. >> 6) Disable non-access TLB warning in handle_nadtlb_fault. Warning >> happens occassionally handling flushes for COW faults. >> 7) Remove flush_cache_dup_mm. >> 8) Flush entire cache in flush_cache_mm and flush_cache_range on >> processors with aliasing caches. Only flush small cache ranges >> on machines with PA8800/PA8900 processors. >> 9) Tested on rp3440, c8000 and c3750. > > Given how long these changelogs are, and how fragile the whole caching is I > think it is a good idea to split this patch into smaller ones, to improve > readability and being able to bisect it. FWIW, I've done some cleanups to this patch and committed it to my for-next tree. In case it's split up, please use the revised version. Helge
