Le 19/01/2022 à 02:15, Kefeng Wang a écrit : > > On 2022/1/11 14:04, Christophe Leroy wrote: >> >> Le 11/01/2022 à 05:37, Nicholas Piggin a écrit : >>> Excerpts from Kefeng Wang's message of January 8, 2022 9:58 pm: >>>> Hi PPC maintainers， ping.. >>> Hmm. I might have confused myself about this. I'm going back and >>> trying to work out what I was thinking when I suggested it. This >>> works on 64e because vmalloc space is below the kernel linear map, >>> right? >>> >>> On 64s it is the other way around and it is still possible to enable >>> flatmem on 64s. Altough we might just not hit the problem there because >>> __pa() will not mask away the vmalloc offset for 64s so it will still >>> return something that's outside the pfn_valid range for flatmem. That's >>> very subtle though. >> That's the way it works on PPC32 at least, so for me it's not chocking >> to have it work the same way on PPC64s. >> >> The main issue here is the way __pa() works. On PPC32 __pa = va - >> PAGE_OFFSET, so it works correctly for any address. >> On PPC64, __pa() works by masking out the 2 top bits instead of >> substracting PAGE_OFFSET, so the test must add a verification that we >> really have the 2 top bits set at first. This is what (addr >= >> PAGE_OFFSET) does. Once this first test is done, we can perfectly rely >> on pfn_valid() just like PPC32, I see absolutely no point in an >> additionnal test checking the addr is below KERN_VIRT_START. > > > Hi Christophe and Nicholas， for ppc32， I think we need check the upper > limit, Why ? Have you experimented any problem at all on PPC32 with the way it is done at the moment ? I don't think we have to change PPC32 at all unless we have a real reason to do it. > > eg, addr >= PAGE_OFFSET && addr < high_memory Isn't it exactly what pfn_valid() already do today ? Why change that at all ? Christophe > > arch/powerpc/mm/mem.c: high_memory = (void *) __va(max_low_pfn * > PAGE_SIZE); > > for ppc32 max_low_pfn is the upper low memory pfn, and For ppc64, > high_memory is > > the max memory pfn, it looks good too, correct me if I'm wrong, if the > above check > > is ok, I will send a new v3, thanks. > > > > >> >> >>> The checks added to __pa actually don't prevent vmalloc memory from >>> being passed to it either on 64s, only a more basic test. >> That's correct. It is the role of pfn_valid() to check that. >> >> Christophe >> >>> I think 64s wants (addr >= PAGE_OFFSET && addr < KERN_VIRT_START) as >>> the condition. Could possibly add that check to __pa as well to >>> catch vmalloc addresses. >>> >>> Thanks, >>> Nick >>> >>>
