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    SubjectRe: [PATCH v3 2/4] arm64: mte: Add asynchronous mode support
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    On 1/15/21 3:13 PM, Mark Rutland wrote:
    > On Fri, Jan 15, 2021 at 12:00:41PM +0000, Vincenzo Frascino wrote:
    >> MTE provides an asynchronous mode for detecting tag exceptions. In
    >> particular instead of triggering a fault the arm64 core updates a
    >> register which is checked by the kernel after the asynchronous tag
    >> check fault has occurred.
    >>
    >> Add support for MTE asynchronous mode.
    >>
    >> The exception handling mechanism will be added with a future patch.
    >>
    >> Note: KASAN HW activates async mode via kasan.mode kernel parameter.
    >> The default mode is set to synchronous.
    >> The code that verifies the status of TFSR_EL1 will be added with a
    >> future patch.
    >>
    >> Cc: Catalin Marinas <catalin.marinas@arm.com>
    >> Cc: Will Deacon <will@kernel.org>
    >> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    >> ---
    >> arch/arm64/kernel/mte.c | 26 ++++++++++++++++++++++++--
    >> 1 file changed, 24 insertions(+), 2 deletions(-)
    >>
    >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
    >> index 53a6d734e29b..df7a1ae26d7c 100644
    >> --- a/arch/arm64/kernel/mte.c
    >> +++ b/arch/arm64/kernel/mte.c
    >> @@ -153,8 +153,30 @@ void mte_init_tags(u64 max_tag)
    >>
    >> void mte_enable_kernel(enum kasan_hw_tags_mode mode)
    >> {
    >> - /* Enable MTE Sync Mode for EL1. */
    >> - sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
    >> + const char *m;
    >> +
    >> + /* Preset parameter values based on the mode. */
    >> + switch (mode) {
    >> + case KASAN_HW_TAGS_ASYNC:
    >> + /* Enable MTE Async Mode for EL1. */
    >> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_ASYNC);
    >> + m = "asynchronous";
    >> + break;
    >> + case KASAN_HW_TAGS_SYNC:
    >> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
    >> + m = "synchronous";
    >> + break;
    >> + default:
    >> + /*
    >> + * kasan mode should be always set hence we should
    >> + * not reach this condition.
    >> + */
    >> + WARN_ON_ONCE(1);
    >> + return;
    >> + }
    >> +
    >> + pr_info_once("MTE: enabled in %s mode at EL1\n", m);
    >> +
    >> isb();
    >> }
    >
    > For clarity, we should have that ISB before the pr_info_once().
    >

    Good point, I will fix it in v4.

    > As with my comment on patch 1, I think with separate functions this
    > would be much clearer and simpler:
    >
    > static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
    > {
    > sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
    > isb();
    >
    > pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
    > }
    >
    > void mte_enable_kernel_sync(void)
    > {
    > __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
    > }
    >
    > void mte_enable_kernel_async(void)
    > {
    > __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
    > }
    >

    Ok, seems cleaner like this, will adapt my code accordingly.

    > Thanks,
    > Mark.
    >

    --
    Regards,
    Vincenzo

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