On 3/13/20 6:59 AM, Rémi Denis-Courmont wrote: > For proper storage and checking of memory tags, MTE == 2 would be > necessary. I have some code (on top of this RFC but not included) to add the > tag allocation logic. But I have no clue how to actually store the tags in > QEMU > system mode at this point, so it's mostly dead code.
I have implemented this, and posted version 6 yesterday. Peter gave you the link. > In user mode, it seems impossible anyway, as tags are indexed by physical, not > virtual address and QEMU cannot know which virtual memory address may > physically alias another within the user process. I have implemented this as well, with a made-up ABI controlled by a command-line option, which only works with non-shared memory. Because the memory is non-shared, we know a priori that it does not alias another address. Version 5 was posted in October: https://patchew.org/QEMU/20191015163507.12153-1-richard.hender...@linaro.org/ My branch referenced in that cover letter is still available. You will be interested to follow the Linux kernel development of this feature and the user-space ABI: http://lists.infradead.org/pipermail/linux-arm-kernel/2020-February/714413.html In particular, only anonymous memory and files in filesystems backed by ram will be supported. Userspace will get an error if they attempt to enable PROT_MTE on a VMA that does not support tags. When I update my mte user branch, I will only support anonymous memory, since I cannot share my on-the-side data structure for tags between aarch64-linux-user processes, whether or not they are in a tmpfs filesystem. r~
