On Fri, Aug 16, 2019 at 10:21:41AM -0700, Dan Williams wrote: > > We can do a get_dev_pagemap inside the page_walk and touch the pgmap, > > or we can do the 'device mutex && retry' pattern and touch the pgmap > > in the driver, under that lock. > > > > However in all cases the current get_dev_pagemap()'s in the page walk > > are not necessary, and we can delete them. > > Yes, as long as 'struct page' instances resulting from that lookup are > not passed outside of that lock. Indeed. Also, I was reflecting over lunch that the hmm_range_fault should only return DEVICE_PRIVATE pages for the caller's device (see other thread with HCH), and in this case, the caller should also be responsible to ensure that the driver is not calling hmm_range_fault at the same time it is deleting it's own DEVICE_PRIVATE mapping - ie by fencing its page fault handler. This does not apply to PCI_P2PDMA, but, lets see how that looks when we get there. So the whole thing seems pretty safe. Jason
