On Wed, Aug 07, 2019 at 04:53:21PM +0100, Catalin Marinas wrote: > From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > > On arm64 the TCR_EL1.TBI0 bit has been always enabled hence > the userspace (EL0) is allowed to set a non-zero value in the > top byte but the resulting pointers are not allowed at the > user-kernel syscall ABI boundary. > > With the relaxed ABI proposed in this set, it is now possible to pass > tagged pointers to the syscalls, when these pointers are in memory > ranges obtained by an anonymous (MAP_ANONYMOUS) mmap(). > > Relax the requirements described in tagged-pointers.rst to be compliant > with the behaviours guaranteed by the ARM64 Tagged Address ABI. > > Cc: Will Deacon <will.deacon@xxxxxxx> > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > Cc: Szabolcs Nagy <szabolcs.nagy@xxxxxxx> > Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx> > Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > [catalin.marinas@xxxxxxx: minor tweaks] > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > --- > Documentation/arm64/tagged-pointers.rst | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > index 2acdec3ebbeb..82a3eff71a70 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -20,7 +20,8 @@ Passing tagged addresses to the kernel > -------------------------------------- > > All interpretation of userspace memory addresses by the kernel assumes > -an address tag of 0x00. > +an address tag of 0x00, unless the application enables the AArch64 > +Tagged Address ABI explicitly. I think we should have the link to Documentation/arm64/tagged-address-abi.rst here so people see it when it's first referenced. > +The AArch64 Tagged Address ABI description and the guarantees it > +provides can be found in: Documentation/arm64/tagged-address-abi.rst. Then this sentence can be dropped. Will
