On Mon, Jan 25, 2016 at 9:33 AM, Andy Lutomirski <l...@amacapital.net> wrote: > On Mon, Jan 25, 2016 at 9:25 AM, Matthew Wilcox > <matthew.r.wil...@intel.com> wrote: >> From: Matthew Wilcox <wi...@linux.intel.com> >> >> track_pfn_insert() overwrites the pgprot that is passed in with a value >> based on the VMA's page_prot. This is a problem for people trying to >> do clever things with the new vm_insert_pfn_prot() as it will simply >> overwrite the passed protection flags. If we use the current value of >> the pgprot as the base, then it will behave as people are expecting. >> >> Also fix track_pfn_remap() in the same way. > > Well that's embarrassing. Presumably it worked for me because I only > overrode the cacheability bits and lookup_memtype did the right thing. > > But shouldn't the PAT code change the memtype if vm_insert_pfn_prot > requests it? Or are there no callers that actually need that? (HPET > doesn't, because there's a plain old ioremapped mapping.) >
Looking a bit further, track_pfn_remap does this, while track_pfn_insert does not. I don't know why I'm also a bit confused as to how any of this works. There doesn't seem to be any reference counting of memtypes, so I don't understand why, say, remapping the same range twice and then freeing them in FIFO order doesn't break the memtype code. (There's VM_PAT, but that seems likely to be extremely fragile.) --Andy
