From: Dave Hansen <dave.han...@linux.intel.com> Date: Wed, 11 Jan 2017 10:13:54 -0800
> For memory shared by two different processes, do they have to agree on > what the tags are, or can they differ? Whoever allocates the memory (does the mmap()+mprotect() or whatever), decides on the tag. They set it, and this determines which virtual address is valid to access that mapping. It's like kmalloc() returns pointers with some weird bits set in the upper bits of the address. Behind the scenes kmalloc() sets the TAG bits appropriately. It doesn't, in that sense, matter where in the non-tagged virtual address space the memory is mapped. All that matters is that, for a given page, the TAG bits in the virtual address used for loads and stores to that mapping are set properly. I think the fundamental thing being missed is that the TAG bits in the virtual address are not interpreted by the TLB. They are chopped off before virtual address translation occurs. The TAG bits of the virtual address serve only to indicate what ADI value the load or store thinks is valid to use for access to that piece of memory. Or something like that... :-)
