On 11/25/2017 07:45 PM, Helge Deller wrote: > On 22.11.2017 20:53, Matthew Wilcox wrote: >> On Wed, Nov 22, 2017 at 08:52:37AM -0800, Dan Williams wrote: >>> On Wed, Nov 22, 2017 at 4:02 AM, Vlastimil Babka <vbabka@xxxxxxx> wrote: >>>> On 11/01/2017 04:36 PM, Jan Kara wrote: >>>>> From: Dan Williams <dan.j.williams@xxxxxxxxx> >>>>> >>>>> The mmap(2) syscall suffers from the ABI anti-pattern of not validating >>>>> unknown flags. However, proposals like MAP_SYNC need a mechanism to >>>>> define new behavior that is known to fail on older kernels without the >>>>> support. Define a new MAP_SHARED_VALIDATE flag pattern that is >>>>> guaranteed to fail on all legacy mmap implementations. >>>> >>>> So I'm trying to make sense of this together with Michal's attempt for >>>> MAP_FIXED_SAFE [1] where he has to introduce a completely new flag >>>> instead of flag modifier exactly for the reason of not validating >>>> unknown flags. And my conclusion is that because MAP_SHARED_VALIDATE >>>> implies MAP_SHARED and excludes MAP_PRIVATE, MAP_FIXED_SAFE as a >>>> modifier cannot build on top of this. Wouldn't thus it be really better >>>> long-term to introduce mmap3 at this point? ... >>> >>> We have room to define MAP_PRIVATE_VALIDATE in MAP_TYPE on every arch >>> except parisc. Can we steal an extra bit for MAP_TYPE from somewhere >>> else on parisc? >> >> It looks like 0x08 should work. > > I posted an RFC to the parisc mailing list for that: > https://patchwork.kernel.org/patch/9970553/ Thanks. BTW there doesn't seem to be much interest making MAP_FIXED_SAFE a flag modifier after all, so MAP_PRIVATE_VALIDATE wouldn't get immediate users. > Basically this is (for parisc only): > -#define MAP_TYPE 0x03 /* Mask for type of mapping */ > +#define MAP_TYPE (MAP_SHARED|MAP_PRIVATE|MAP_RESRVD1|MAP_RESRVD2) /* Mask for type of mapping */ > #define MAP_FIXED 0x04 /* Interpret addr exactly */ > +#define MAP_RESRVD1 0x08 /* reserved for 3rd bit of MAP_TYPE */ > #define MAP_ANONYMOUS 0x10 /* don't use a file */ > +#define MAP_RESRVD2 0x20 /* reserved for 4th bit of MAP_TYPE */ > >> But I don't have an HPUX machine around >> to check that HP didn't use that bit for something else. > > We completely dropped support for HPUX binaries, so it's not relvant any longer. > >> It'd probably help to cc the linux-parisc mailing list when asking >> questions about PARISC, eh? > > Yes, please. > > Helge >
