linux-kernel - Re: [PATCH v3 3/6] arm64: KVM: Add iflag for FEAT

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Message-ID: <71007f96-da57-4554-b939-a862e97adb37@arm.com>
Date:   Thu, 16 Nov 2023 19:27:10 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        maz@...nel.org
Cc:     broonie@...nel.org, Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Rob Herring <robh@...nel.org>,
        Jintack Lim <jintack.lim@...aro.org>,
        Fuad Tabba <tabba@...gle.com>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Akihiko Odaki <akihiko.odaki@...nix.com>,
        Joey Gouly <joey.gouly@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/6] arm64: KVM: Add iflag for FEAT_TRF

On 19/10/2023 17:55, James Clark wrote:
> Add an extra iflag to signify if the TRFCR register is accessible.
> Because TRBE requires FEAT_TRF, DEBUG_STATE_SAVE_TRBE still has the same
> behavior even though it's only set when FEAT_TRF is present.
> 
> The following holes are left in struct kvm_vcpu_arch, but there aren't
> enough other 8 bit fields to rearrange it to leave any hole smaller than
> 7 bytes:
> 
>    u8                         cflags;               /*  2292     1 */
>    /* XXX 1 byte hole, try to pack */
>    u16                        iflags;               /*  2294     2 */
>    u8                         sflags;               /*  2296     1 */
>    bool                       pause;                /*  2297     1 */
>    /* XXX 6 bytes hole, try to pack */
> 
> Signed-off-by: James Clark <james.clark@....com>

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>


> ---
>   arch/arm64/include/asm/kvm_host.h |  4 +++-
>   arch/arm64/kvm/debug.c            | 22 ++++++++++++++++++----
>   2 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7c82927ddaf2..0f0bf8e641bd 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -535,7 +535,7 @@ struct kvm_vcpu_arch {
>   	u8 cflags;
>   
>   	/* Input flags to the hypervisor code, potentially cleared after use */
> -	u8 iflags;
> +	u16 iflags;
>   
>   	/* State flags for kernel bookkeeping, unused by the hypervisor code */
>   	u8 sflags;
> @@ -741,6 +741,8 @@ struct kvm_vcpu_arch {
>   #define DEBUG_STATE_SAVE_TRBE	__vcpu_single_flag(iflags, BIT(6))
>   /* vcpu running in HYP context */
>   #define VCPU_HYP_CONTEXT	__vcpu_single_flag(iflags, BIT(7))
> +/* Save trace filter controls */
> +#define DEBUG_STATE_SAVE_TRFCR	__vcpu_single_flag(iflags, BIT(8))
>   
>   /* SVE enabled for host EL0 */
>   #define HOST_SVE_ENABLED	__vcpu_single_flag(sflags, BIT(0))
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 8725291cb00a..20cdd40b3c42 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -331,14 +331,28 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
>   	    !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(PMBIDR_EL1_P_SHIFT)))
>   		vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_SPE);
>   
> -	/* Check if we have TRBE implemented and available at the host */
> -	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
> -	    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
> -		vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
> +	/*
> +	 * Save TRFCR on nVHE if FEAT_TRF (TraceFilt) exists. This will be
> +	 * done in cases where use of TRBE doesn't completely disable trace and
> +	 * handles the exclude_host/exclude_guest rules of the trace session.
> +	 */
> +	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceFilt_SHIFT)) {
> +		vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
> +		/*
> +		 * Check if we have TRBE implemented and available at the host. If it's
> +		 * in use at the time of guest switch it will need to be disabled and
> +		 * then restored. The architecture mandates FEAT_TRF with TRBE, so we
> +		 * only need to check for TRBE after TRF.
> +		 */
> +		if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
> +		    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
> +			vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
> +	}
>   }
>   
>   void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
>   {
>   	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
>   	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
> +	vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
>   }