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Message-ID: <87edihmgfm.wl-maz@kernel.org>
Date: Fri, 29 Sep 2023 11:17:49 +0100
From: Marc Zyngier <maz@...nel.org>
To: James Clark <james.clark@....com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev, broonie@...nel.org, suzuki.poulose@....com,
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>,
Joey Gouly <joey.gouly@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/5] arm64: KVM: Add interface to set guest value for TRFCR register
On Thu, 28 Sep 2023 16:16:07 +0100,
James Clark <james.clark@....com> wrote:
>
> Add an interface for the Coresight driver to use to set the value of the
> TRFCR register for the guest. This register controls the exclude
> settings for trace at different exception levels, and is used to
> honor the exclude_host and exclude_guest parameters from the Perf
> session. This will be used to later write TRFCR_EL1 on nVHE at guest
> switch. For VHE, TRFCR_EL1 is written immediately. Because guest writes
> to the register are trapped, the value will persist and can't be
> modified.
>
> The settings must be copied to the vCPU before each run in the same
> way that PMU events are because the per-cpu struct isn't accessible in
> protected mode.
>
> Now that both guest and host values are saved, rename trfcr_el1 to
> host_trfcr_el1 to make it clear that's the value that should be restored
> on return to the host.
>
> Reviewed-by: Mark Brown <broonie@...nel.org> (sysreg)
> Signed-off-by: James Clark <james.clark@....com>
> ---
> arch/arm64/include/asm/kvm_host.h | 6 +++++-
> arch/arm64/kvm/arm.c | 1 +
> arch/arm64/kvm/debug.c | 21 +++++++++++++++++++++
> arch/arm64/kvm/hyp/nvhe/debug-sr.c | 4 ++--
> arch/arm64/tools/sysreg | 4 ++++
> 5 files changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 498f922f4f41..0e57827a0cf2 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -547,7 +547,8 @@ struct kvm_vcpu_arch {
> /* Statistical profiling extension */
> u64 pmscr_el1;
> /* Self-hosted trace */
> - u64 trfcr_el1;
> + u64 host_trfcr_el1;
> + u64 guest_trfcr_el1;
> } host_debug_state;
I think it is high time we stop having *guest* state in a structure
that is obviously for the host, starting by moving the breakpoint and
watchpoint out, and into the sysreg array.
And then TRFCR_EL1 can join the fun. But it is pretty unclear whether
that's actually the guest state.
>
> /* VGIC state */
> @@ -1097,6 +1098,8 @@ void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu);
> void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr);
> void kvm_clr_pmu_events(u32 clr);
> bool kvm_set_pmuserenr(u64 val);
> +void kvm_etm_set_guest_trfcr(u64 trfcr_guest);
> +void kvm_etm_update_vcpu_events(struct kvm_vcpu *vcpu);
> #else
> static inline void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr) {}
> static inline void kvm_clr_pmu_events(u32 clr) {}
> @@ -1104,6 +1107,7 @@ static inline bool kvm_set_pmuserenr(u64 val)
> {
> return false;
> }
> +static inline void kvm_etm_set_guest_trfcr(u64 trfcr_guest) {}
> #endif
>
> void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 1bfdd583b261..65e805dc1d7a 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -958,6 +958,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
> kvm_vgic_flush_hwstate(vcpu);
>
> kvm_pmu_update_vcpu_events(vcpu);
> + kvm_etm_update_vcpu_events(vcpu);
>
> /*
> * Ensure we set mode to IN_GUEST_MODE after we disable
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 6a1bad1a921b..379d2677961f 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -22,6 +22,7 @@
> DBG_MDSCR_MDE)
>
> static DEFINE_PER_CPU(u64, mdcr_el2);
> +static DEFINE_PER_CPU(u64, guest_trfcr);
Hold on a sec. Why is that global? I'd expect the tracing to be
specific to a vcpu, and not to affect *everything*.
>
> /**
> * save/restore_guest_debug_regs
> @@ -342,3 +343,23 @@ 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_TRFCR);
> }
> +
> +void kvm_etm_set_guest_trfcr(u64 trfcr_guest)
> +{
> + if (has_vhe())
> + write_sysreg_s(trfcr_guest, SYS_TRFCR_EL12);
> + else
> + *this_cpu_ptr(&guest_trfcr) = trfcr_guest;
> +}
> +EXPORT_SYMBOL_GPL(kvm_etm_set_guest_trfcr);
In what context can this be called? What if we want to expose TRFCR to
guests instead? It looks to me that this ultimately precludes such
use.
> +
> +/*
> + * Updates the vcpu's view of the etm events for this cpu. Must be
> + * called before every vcpu run after disabling interrupts, to ensure
> + * that an interrupt cannot fire and update the structure.
> + */
> +void kvm_etm_update_vcpu_events(struct kvm_vcpu *vcpu)
> +{
> + if (!has_vhe() && vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
> + vcpu->arch.host_debug_state.guest_trfcr_el1 = *this_cpu_ptr(&guest_trfcr);
But what is the point of this per-vcpu field if all you care about is
some per-CPU data?
> +}
> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> index 89c208112eb7..55bc01e9808f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> @@ -86,7 +86,7 @@ void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> __debug_save_spe(&vcpu->arch.host_debug_state.pmscr_el1);
> /* Disable and flush Self-Hosted Trace generation */
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
> - __debug_save_trace(&vcpu->arch.host_debug_state.trfcr_el1);
> + __debug_save_trace(&vcpu->arch.host_debug_state.host_trfcr_el1);
> }
`<>
> void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> @@ -99,7 +99,7 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_SPE))
> __debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
> - __debug_restore_trace(vcpu->arch.host_debug_state.trfcr_el1);
> + __debug_restore_trace(vcpu->arch.host_debug_state.host_trfcr_el1);
> }
>
> void __debug_switch_to_host(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index 992722c0c23b..295a4a625b8b 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -2661,3 +2661,7 @@ EndSysreg
> Sysreg TRFCR_EL2 3 4 1 2 1
> Fields TRFCR_EL2
> EndSysreg
> +
> +Sysreg TRFCR_EL12 3 5 1 2 1
> +Fields TRFCR_ELx
> +EndSysreg
Please move this to the first patch.
M.
--
Without deviation from the norm, progress is not possible.
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