Re: [PATCH 00/22] arm64: Memory Tagging Extension user-space support

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Dec 13, 2019 at 10:05:10AM -0800, Peter Collingbourne wrote:
> On Wed, Dec 11, 2019 at 10:40 AM Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> > This series proposes the initial user-space support for the ARMv8.5
> > Memory Tagging Extension [1].
> 
> Thanks for sending out this series. I have been testing it on Android
> with the FVP model and my in-development scudo changes that add memory
> tagging support [1], and have not noticed any problems so far.

Thanks for the comments so far and the testing. I'll post a v2 next
week.

> > - Clarify whether mmap(tagged_addr, PROT_MTE) pre-tags the memory with
> >   the tag given in the tagged_addr hint. Strong justification is
> >   required for this as it would force arm64 to disable the zero page.
> 
> We would like to use this feature in scudo to tag large (>128KB on
> Android) allocations, which are currently allocated via mmap rather
> than from an allocation pool. Otherwise we would need to pay the cost
> (perf and RSS) of faulting all of their pages at allocation time
> instead of on demand, if we want to tag them.

Would the default tag of 0 be sufficient here? We disable match-all for
user-space already, so 0 is not a wildcard.

-- 
Catalin