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

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Message-ID: <d0daf831-3340-87f2-a021-0b775ce7af2a@arm.com>
Date:   Thu, 28 Jan 2021 09:34:11 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Marc Zyngier <maz@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        mathieu.poirier@...aro.org, 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 1/27/21 9:58 AM, Marc Zyngier wrote:
> 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 for the heads up. We will need to see how things get merged.
Ideally this patch and the previous one (TRBE definitions could go
via the arm64 tree / kvm tree), in which case we could rebase these
two patches on the respective tree.

Cheers
Suzuki