Re: [PATCH v8 32/43] arm64: mte: Switch GCR_EL1 in kernel entry and exit

[Andrey Konovalov <andreyknvl@google.com>]

On Thu, Nov 5, 2020 at 6:30 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Thu, Nov 05, 2020 at 12:18:47AM +0100, Andrey Konovalov wrote:
> > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > index 14b0c19a33e3..cc7e0f8707f7 100644
> > --- a/arch/arm64/kernel/mte.c
> > +++ b/arch/arm64/kernel/mte.c
> > @@ -23,6 +23,8 @@
> >  #include <asm/ptrace.h>
> >  #include <asm/sysreg.h>
> >
> > +u64 gcr_kernel_excl __ro_after_init;
> > +
> >  static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
> >  {
> >       pte_t old_pte = READ_ONCE(*ptep);
> > @@ -123,6 +125,23 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
> >
> >  void __init mte_init_tags(u64 max_tag)
> >  {
> > +     static bool gcr_kernel_excl_initialized = false;
> > +
> > +     if (!gcr_kernel_excl_initialized) {
> > +             /*
> > +              * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
> > +              * This conversion extracts an MTE tag from a KASAN tag.
> > +              */
> > +             u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
> > +                                          max_tag), 0);
> > +
> > +             gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
> > +             gcr_kernel_excl_initialized = true;
> > +     }
> > +
> > +     /* Enable the kernel exclude mask for random tags generation. */
> > +     write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
>
> Same question as on a previous patch. Is SYS_GCR_EL1 written on the
> other registers via cpu_enable_mte()?

You mean for other CPUs? mte_init_tags() is called for each CPU if
that's what you mean. Otherwise, please clarify the question.