[PATCH] KVM: arm64: permit MAP_SHARED mappings with MTE enabled

[Cornelia Huck]

On Fri, Jul 08 2022, Peter Xu <peterx at redhat.com> wrote:

> On Fri, Jul 08, 2022 at 03:03:34PM +0200, Cornelia Huck wrote:

>> I was thinking about a new flag that implies "copy metadata"; not sure
>> how we would get the same atomicity with a separate ioctl. I've only
>> just started looking at userfaultfd, though, and I might be on a wrong
>> track... One thing I'd like to avoid is having something that is too
>> ARM-specific, I think there are other architecture features that might
>> have similar issues.
>
> Agreed, to propose such an interface we'd better make sure it'll be easily
> applicable to other similar memory protection mechanisms elsewhere.

There's storage keys on s390, although I believe they are considered
legacy by now. I dimly recall something in x86 land.

>
>> 
>> Maybe someone more familiar with uffd and/or postcopy can chime in?
>
> Hanving UFFDIO_COPY provide a new flag sounds reasonable to me.  I'm
> curious what's the maximum possible size of the tags and whether they can
> be embeded already into struct uffdio_copy somehow.

Each tag is four bits and covers 16 bytes (also see the defs in
arch/arm64/include/asm/mte-def.h).