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

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