[PATCH v2 2/3] arm64: mte: handle tags zeroing at page allocation time

[Catalin Marinas]

On Tue, May 11, 2021 at 04:54:25PM -0700, Peter Collingbourne wrote:
> Currently, on an anonymous page fault, the kernel allocates a zeroed
> page and maps it in user space. If the mapping is tagged (PROT_MTE),
> set_pte_at() additionally clears the tags. It is, however, more
> efficient to clear the tags at the same time as zeroing the data on
> allocation. To avoid clearing the tags on any page (which may not be
> mapped as tagged), only do this if the vma flags contain VM_MTE. This
> requires introducing a new GFP flag that is used to determine whether
> to clear the tags.
> 
> The DC GZVA instruction with a 0 top byte (and 0 tag) requires
> top-byte-ignore. Set the TCR_EL1.{TBI1,TBID1} bits irrespective of
> whether KASAN_HW is enabled.
> 
> Signed-off-by: Peter Collingbourne <pcc at google.com>
> Co-developed-by: Catalin Marinas <catalin.marinas at arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> Link: https://linux-review.googlesource.com/id/Id46dc94e30fe11474f7e54f5d65e7658dbdddb26

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>