linux-kernel - Re: [PATCH V3 10/14] arm64: nvhe: Allow TRBE access at EL1

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Message-ID: <12b1572e2568d4936f0458649065fe64@kernel.org>
Date:   Wed, 27 Jan 2021 09:58:15 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        mathieu.poirier@...aro.org, suzuki.poulose@....com,
        mike.leach@...aro.org, lcherian@...vell.com,
        linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH V3 10/14] arm64: nvhe: Allow TRBE access at EL1

On 2021-01-27 08:55, Anshuman Khandual wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> When the kernel is booted at EL2 in a nvhe configuration,
> enable the TRBE access to the EL1. The EL1 still can't trace
> EL2, unless EL2 permits explicitly via TRFCR_EL2.E2TRE.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> cc: Anshuman Khandual <anshuman.khandual@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>

Acked-by: Marc Zyngier <maz@...nel.org>

One comment below, though:

> ---
>  arch/arm64/include/asm/el2_setup.h | 19 +++++++++++++++++++
>  arch/arm64/include/asm/kvm_arm.h   |  2 ++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/el2_setup.h
> b/arch/arm64/include/asm/el2_setup.h
> index a7f5a1b..05ecce9 100644
> --- a/arch/arm64/include/asm/el2_setup.h
> +++ b/arch/arm64/include/asm/el2_setup.h
> @@ -72,6 +72,25 @@
>  .endif
> 
>  3:
> +
> +.ifeqs	"\mode", "nvhe"
> +	/*
> +	 * If the Trace Buffer is available, allow
> +	 * the EL1 to own it. Note that EL1 cannot
> +	 * trace the EL2, as it is prevented by
> +	 * TRFCR_EL2.E2TRE == 0.
> +	 */
> +	ubfx	x0, x1, #ID_AA64DFR0_TRBE_SHIFT, #4
> +	cbz	x0, 1f
> +
> +	mrs_s	x0, SYS_TRBIDR_EL1
> +	and	x0, x0, TRBIDR_PROG
> +	cbnz	x0, 1f
> +	mov	x0, #(MDCR_EL2_E2TB_EL1_OWN << MDCR_EL2_E2TB_SHIFT)
> +	orr	x2, x2, x0
> +.endif
> +
> +1:

Note that this will (badly) conflict with the late-VHE patches[1],
where this code path has been reworked.

Thanks,

         M.

[1] https://lore.kernel.org/r/20210125105019.2946057-1-maz@kernel.org
-- 
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