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Message-ID: <f30f3b77-0c72-49ab-8d30-48ba642ba0e8@arm.com>
Date: Mon, 29 Jan 2024 12:20:08 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
will@...nel.org, catalin.marinas@....com, mark.rutland@....com
Cc: Mark Brown <broonie@...nel.org>, James Clark <james.clark@....com>,
Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-perf-users@...r.kernel.org, Oliver Upton <oliver.upton@...ux.dev>,
James Morse <james.morse@....com>, kvmarm@...ts.linux.dev
Subject: Re: [PATCH V16 5/8] KVM: arm64: nvhe: Disable branch generation in
nVHE guests
On 25/01/2024 09:41, Anshuman Khandual wrote:
> Disable the BRBE before we enter the guest, saving the status and enable it
> back once we get out of the guest. This avoids capturing branch records in
> the guest kernel or userspace, which would be confusing the host samples.
>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Oliver Upton <oliver.upton@...ux.dev>
> Cc: James Morse <james.morse@....com>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: kvmarm@...ts.linux.dev
> Cc: linux-arm-kernel@...ts.infradead.org
> CC: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Changes in V16:
>
> - Dropped BRBCR_EL1 and BRBFCR_EL1 from enum vcpu_sysreg
> - Reverted back the KVM NVHE patch - used host_debug_state based 'brbcr_el1'
> element, and dropped the previous dependency on Jame's coresight series
>
> arch/arm64/include/asm/kvm_host.h | 5 ++++-
> arch/arm64/kvm/debug.c | 5 +++++
> arch/arm64/kvm/hyp/nvhe/debug-sr.c | 33 ++++++++++++++++++++++++++++++
> 3 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 21c57b812569..bce8792092af 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -569,7 +569,7 @@ 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;
> @@ -610,6 +610,7 @@ struct kvm_vcpu_arch {
> u64 pmscr_el1;
> /* Self-hosted trace */
> u64 trfcr_el1;
> + u64 brbcr_el1;
> } host_debug_state;
>
> /* VGIC state */
> @@ -779,6 +780,8 @@ 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 BRBE context if active */
> +#define DEBUG_STATE_SAVE_BRBE __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..99f85d8acbf3 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -335,10 +335,15 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
> 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);
> +
> + /* Check if we have BRBE implemented and available at the host */
> + if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_BRBE_SHIFT))
> + vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_BRBE);
> }
>
> 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_BRBE);
> }
> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> index 4558c02eb352..79bcf0fb1326 100644
> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> @@ -79,6 +79,34 @@ static void __debug_restore_trace(u64 trfcr_el1)
> write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1);
> }
>
> +static void __debug_save_brbe(u64 *brbcr_el1)
> +{
> + *brbcr_el1 = 0;
> +
> + /* Check if the BRBE is enabled */
> + if (!(read_sysreg_s(SYS_BRBCR_EL1) & (BRBCR_ELx_E0BRE | BRBCR_ELx_ExBRE)))
> + return;
> +
> + /*
> + * Prohibit branch record generation while we are in guest.
> + * Since access to BRBCR_EL1 is trapped, the guest can't
> + * modify the filtering set by the host.
> + */
> + *brbcr_el1 = read_sysreg_s(SYS_BRBCR_EL1);
> + write_sysreg_s(0, SYS_BRBCR_EL1);
> + isb();
Is this isb() required here ? This can be synchronised with the Guest
entry ?
> +}
> +
> +static void __debug_restore_brbe(u64 brbcr_el1)
> +{
> + if (!brbcr_el1)
> + return;
> +
> + /* Restore BRBE controls */
> + write_sysreg_s(brbcr_el1, SYS_BRBCR_EL1);
> + isb();
Similarly here, exit back to EL1 host can synchronise the setting ?
Suzuki
> +}
> +
> void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> {
> /* Disable and flush SPE data generation */
> @@ -87,6 +115,9 @@ void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> /* Disable and flush Self-Hosted Trace generation */
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
> __debug_save_trace(&vcpu->arch.host_debug_state.trfcr_el1);
> + /* Disable BRBE branch records */
> + if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_BRBE))
> + __debug_save_brbe(&vcpu->arch.host_debug_state.brbcr_el1);
> }
>
> void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> @@ -100,6 +131,8 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> __debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
> __debug_restore_trace(vcpu->arch.host_debug_state.trfcr_el1);
> + if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_BRBE))
> + __debug_restore_brbe(vcpu->arch.host_debug_state.brbcr_el1);
> }
>
> void __debug_switch_to_host(struct kvm_vcpu *vcpu)
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