linux-kernel - Re: [PATCH v4 05/19] kvm: arm64: Disable guest access to trace filter controls

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Message-ID: <cbe4ef17-38f9-c555-d838-796be752d4a3@arm.com>
Date:   Mon, 22 Mar 2021 22:24:19 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, anshuman.khandual@....com,
        leo.yan@...aro.org, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 05/19] kvm: arm64: Disable guest access to trace filter
 controls

Hi Marc,

On 25/02/2021 19:35, Suzuki K Poulose wrote:
> Disable guest access to the Trace Filter control registers.
> We do not advertise the Trace filter feature to the guest
> (ID_AA64DFR0_EL1: TRACE_FILT is cleared) already, but the guest
> can still access the TRFCR_EL1 unless we trap it.
> 
> This will also make sure that the guest cannot fiddle with
> the filtering controls set by a nvhe host.
> 
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>

We have already have the v8.4 self hosted tracing support in 5.12-rcX.
Do you think you can pick this up for this 5.12 ?

Cheers
Suzuki

> ---
> New patch
> ---
>   arch/arm64/include/asm/kvm_arm.h | 1 +
>   arch/arm64/kvm/debug.c           | 2 ++
>   2 files changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 4e90c2debf70..94d4025acc0b 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -278,6 +278,7 @@
>   #define CPTR_EL2_DEFAULT	CPTR_EL2_RES1
>   
>   /* Hyp Debug Configuration Register bits */
> +#define MDCR_EL2_TTRF		(1 << 19)
>   #define MDCR_EL2_TPMS		(1 << 14)
>   #define MDCR_EL2_E2PB_MASK	(UL(0x3))
>   #define MDCR_EL2_E2PB_SHIFT	(UL(12))
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 7a7e425616b5..dbc890511631 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -89,6 +89,7 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
>    *  - Debug ROM Address (MDCR_EL2_TDRA)
>    *  - OS related registers (MDCR_EL2_TDOSA)
>    *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
> + *  - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
>    *
>    * Additionally, KVM only traps guest accesses to the debug registers if
>    * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
> @@ -112,6 +113,7 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>   	vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
>   	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
>   				MDCR_EL2_TPMS |
> +				MDCR_EL2_TTRF |
>   				MDCR_EL2_TPMCR |
>   				MDCR_EL2_TDRA |
>   				MDCR_EL2_TDOSA);
>