• Jeffrey Lee's avatar
    Cache maintenance fixes · b0682acb
    Jeffrey Lee authored
      This set of changes tackles two main issues:
      * Before mapping out a cacheable page or making it uncacheable, the OS performs a cache clean+invalidate op. However this leaves a small window where data may be fetched back into the cache, either accidentally (dodgy interrupt handler) or via agressive prefetch (as allowed for by the architecture). This rogue data can then result in coherency issues once the pages are mapped out or made uncacheable a short time later.
        The fix for this is to make the page uncacheable before performing the cache maintenance (although this isn't ideal, as prior to ARMv7 it's implementation defined whether address-based cache maintenance ops affect uncacheable pages or not - and on ARM11 it seems that they don't, so for that CPU we currently force a full cache clean instead)
      * Modern ARMs generally ignore unexpected cache hits, so there's an interrupt hole in the current OS_Memory 0 "make temporarily uncacheable" implementation where the cache is being flushed after the page has been made uncacheable (consider the case of a page that's being used by an interrupt handler, but the page is being made uncacheable so it can also be used by DMA). As well as affecting ARMv7+ devices this was found to affect XScale (and ARM11, although untested for this issue, would have presumably suffered from the "can't clean uncacheable pages" limitation)
        The fix for this is to disable IRQs around the uncache sequence - however FIQs are currently not being dealt with, so there's still a potential issue there.
      File changes:
      - Docs/HAL/ARMop_API, hdr/KernelWS, hdr/OSMisc - Add new Cache_CleanInvalidateRange ARMop
      - s/ARM600, s/VMSAv6 - BangCam updated to make the page uncacheable prior to flushing the cache. Add GetTempUncache macro to help with calculating the page flags required for making pages uncacheable. Fix abort in OS_MMUControl on Raspberry Pi - MCR-based ISB was resetting ZeroPage pointer to 0
      - s/ARMops - Cache_CleanInvalidateRange implementations. PL310 MMU_ChangingEntry/MMU_ChangingEntries refactored to rely on Cache_CleanInvalidateRange_PL310, which should be a more optimal implementation of the cache cleaning code that was previously in MMU_ChangingEntry_PL310.
      - s/ChangeDyn - Rename FastCDA_UpFront to FastCDA_Bulk, since the cache maintenance is no longer performed upfront. CheckCacheabilityR0ByMinusR2 now becomes RemoveCacheabilityR0ByMinusR2. PMP LogOp implementation refactored quite a bit to perform cache/TLB maintenance after making page table changes instead of before. One flaw with this new implementation is that mapping out large areas of cacheable pages will result in multiple full cache cleans while the old implementation would have (generally) only performed one - a two-pass approach over the page list would be needed to solve this.
      - s/GetAll - Change file ordering so GetTempUncache macro is available earlier
      - s/HAL - ROM decompression changed to do full MMU_Changing instead of MMU_ChangingEntries, to make sure earlier cached data is truly gone from the cache. ClearPhysRAM changed to make page uncacheable before flushing cache.
      - s/MemInfo - OS_Memory 0 interrupt hole fix
      - s/AMBControl/memmap - AMB_movepagesout_L2PT now split into cacheable+non-cacheable variants. Sparse map out operation now does two passes through the page list so that they can all be made uncacheable prior to the cache flush + map out.
      Tested on StrongARM, XScale, ARM11, Cortex-A7, Cortex-A9, Cortex-A15, Cortex-A53
      Appears to fix the major issues plaguing SATA on IGEPv5
    Version 5.35, Tagged as 'Kernel-5_35-4_79_2_306'
memmap 33.3 KB