# Re: \[PATCH v2\] sparc64: Add support for Application Data Integrity (ADI) - From: Rob Gardner \ - Date: 2016-03-07 23:17:00 - List: linux-api - Page: https://ratatoskr.run/linux-api/2016/03/4703445 - Thread: https://ratatoskr.run/sparclinux/2016/03/4699675/t.md ```text On 03/07/2016 01:38 PM, David Miller wrote: > From: Khalid Aziz > Date: Mon, 7 Mar 2016 14:33:56 -0700 > >> On 03/07/2016 12:16 PM, David Miller wrote: >>> From: Khalid Aziz >>> Date: Mon, 7 Mar 2016 11:24:54 -0700 >>> >>>> Tags can be cleared by user by setting tag to 0. Tags are >>>> automatically cleared by the hardware when the mapping for a virtual >>>> address is removed from TSB (which is why swappable pages are a >>>> problem), so kernel does not have to do it as part of clean up. >>> You might be able to crib some bits for the Tag in the swp_entry_t, >>> it's >>> 64-bit and you can therefore steal bits from the offset field. >>> >>> That way you'll have the ADI tag in the page tables, ready to >>> re-install >>> at swapin time. >>> >> That is a possibility but limited in scope. An address range covered >> by a single TTE can have large number of tags. Version tags are set on >> cacheline. In extreme case, one could set a tag for each set of >> 64-bytes in a page. Also tags are set completely in userspace and no >> transition occurs to kernel space, so kernel has no idea of what tags >> have been set. I have not found a way to query the MMU on tags. >> >> I will think some more about it. > That would mean that ADI is impossible to use for swappable memory. > > ... > > If that's true I'm extremely disappointed that they devoted so much > silicon and engineering to this feature yet didn't take that one > critical step to make it generally useful. :( You can easily read ADI tags with a simple ldxa #ASI_MCD_PRIMARY instruction. Rob -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org ```