Re: [PATCH v2] sparc64: Add support for Application Data Integrity (ADI)

[Khalid Aziz]

On 03/07/2016 11:09 AM, Rob Gardner wrote:
> On 03/07/2016 10:04 AM, Khalid Aziz wrote:
> > On 03/07/2016 09:56 AM, David Miller wrote:
> > > From: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
> > > Date: Mon, 7 Mar 2016 08:07:53 -0700
> > >
> > > > PR_GET_SPARC_ADICAPS
> > >
> > > Put this into a new ELF auxiliary vector entry via ARCH_DLINFO.
> > >
> > > So now all that's left is supposedly the TAG stuff, please explain
> > > that to me so I can direct you to the correct existing interface to
> > > provide that as well.
> > >
> > > Really, try to avoid prtctl, it's poorly typed and almost worse than
> > > ioctl().
> >
> > The two remaining operations I am looking at are:
> >
> > 1. Is PSTATE.mcde bit set for the process? PR_SET_SPARC_ADI provides
> > this in its return value in the patch I sent.
> >
> > 2. Is TTE.mcd set for a given virtual address? PR_GET_SPARC_ADI_STATUS
> > provides this function in the patch I sent.
> >
> > Setting and clearing version tags can be done entirely from userspace:
> >
> >         while (addr < end) {
> >                 asm volatile(
> >                         "stxa %1, [%0]ASI_MCD_PRIMARY\n\t"
> >                         :
> >                         : "r" (addr), "r" (version));
> >                 addr += adicap.blksz;
> >         }
> > so I do not have to add any kernel code for tags.
>
> What about clearing the tags when the user is done with the memory? You
> can't count on the user to do that, so doesn't the kernel have to do it
> someplace?

Tags can be cleared by user by setting tag to 0. Tags are automatically 
cleared by the hardware when the mapping for a virtual address is 
removed from TSB (which is why swappable pages are a problem), so kernel 
does not have to do it as part of clean up.

Thanks,
Khalid