On 11/11/2021 4:51 PM, Dan Williams wrote: > On Thu, Nov 11, 2021 at 4:30 PM Jane Chu <[email protected]> wrote: >> >> Just a quick update - >> >> I managed to test the 'NP' and 'UC' effect on a pmem dax file. >> The result is, as expected, both setting 'NP' and 'UC' works >> well in preventing the prefetcher from accessing the poisoned >> pmem page. >> >> I injected back-to-back poisons to the 3rd block(512B) of >> the 3rd page in my dax file. With 'NP', the 'mc_safe read' >> stops after reading the 1st and 2nd pages, with 'UC', >> the 'mc_safe read' was able to read [2 pages + 2 blocks] on >> my test machine. > > My expectation is that dax_direct_access() / dax_recovery_read() has > installed a temporary UC alias for the pfn, or has temporarily flipped > NP to UC. Outside of dax_recovery_read() the page will always be NP. >
Okay. Could we only flip the memtype within dax_recovery_read, and not within dax_direct_access? dax_direct_access does not need to access the page. thanks, -jane
