Re: [PATCH v5 07/19] arm64: kvm: Enable access to TRBE support for host

[Mathieu Poirier]

On Tue, Mar 23, 2021 at 12:06:35PM +0000, Suzuki K Poulose wrote:
> For a nvhe host, the EL2 must allow the EL1&0 translation
> regime for TraceBuffer (MDCR_EL2.E2TB == 0b11). This must
> be saved/restored over a trip to the guest. Also, before
> entering the guest, we must flush any trace data if the
> TRBE was enabled. And we must prohibit the generation
> of trace while we are in EL1 by clearing the TRFCR_EL1.
> 
> For vhe, the EL2 must prevent the EL1 access to the Trace
> Buffer.
> 
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Acked-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
>  arch/arm64/include/asm/el2_setup.h | 13 +++++++++
>  arch/arm64/include/asm/kvm_arm.h   |  2 ++
>  arch/arm64/include/asm/kvm_host.h  |  2 ++
>  arch/arm64/kernel/hyp-stub.S       |  3 ++-
>  arch/arm64/kvm/debug.c             |  6 ++---
>  arch/arm64/kvm/hyp/nvhe/debug-sr.c | 42 ++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/switch.c   |  1 +
>  7 files changed, 65 insertions(+), 4 deletions(-)
> 

Marc - do you want me to pick up this one?

> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> index d77d358f9395..bda918948471 100644
> --- a/arch/arm64/include/asm/el2_setup.h
> +++ b/arch/arm64/include/asm/el2_setup.h
> @@ -65,6 +65,19 @@
>  						// use EL1&0 translation.
>  
>  .Lskip_spe_\@:
> +	/* Trace buffer */
> +	ubfx	x0, x1, #ID_AA64DFR0_TRBE_SHIFT, #4
> +	cbz	x0, .Lskip_trace_\@		// Skip if TraceBuffer is not present
> +
> +	mrs_s	x0, SYS_TRBIDR_EL1
> +	and	x0, x0, TRBIDR_PROG
> +	cbnz	x0, .Lskip_trace_\@		// If TRBE is available at EL2
> +
> +	mov	x0, #(MDCR_EL2_E2TB_MASK << MDCR_EL2_E2TB_SHIFT)
> +	orr	x2, x2, x0			// allow the EL1&0 translation
> +						// to own it.
> +
> +.Lskip_trace_\@:
>  	msr	mdcr_el2, x2			// Configure debug traps
>  .endm
>  
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 94d4025acc0b..692c9049befa 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -278,6 +278,8 @@
>  #define CPTR_EL2_DEFAULT	CPTR_EL2_RES1
>  
>  /* Hyp Debug Configuration Register bits */
> +#define MDCR_EL2_E2TB_MASK	(UL(0x3))
> +#define MDCR_EL2_E2TB_SHIFT	(UL(24))
>  #define MDCR_EL2_TTRF		(1 << 19)
>  #define MDCR_EL2_TPMS		(1 << 14)
>  #define MDCR_EL2_E2PB_MASK	(UL(0x3))
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3d10e6527f7d..80d0a1a82a4c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -315,6 +315,8 @@ struct kvm_vcpu_arch {
>  		struct kvm_guest_debug_arch regs;
>  		/* Statistical profiling extension */
>  		u64 pmscr_el1;
> +		/* Self-hosted trace */
> +		u64 trfcr_el1;
>  	} host_debug_state;
>  
>  	/* VGIC state */
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 5eccbd62fec8..05d25e645b46 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -115,9 +115,10 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
>  	mrs_s	x0, SYS_VBAR_EL12
>  	msr	vbar_el1, x0
>  
> -	// Use EL2 translations for SPE and disable access from EL1
> +	// Use EL2 translations for SPE & TRBE and disable access from EL1
>  	mrs	x0, mdcr_el2
>  	bic	x0, x0, #(MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT)
> +	bic	x0, x0, #(MDCR_EL2_E2TB_MASK << MDCR_EL2_E2TB_SHIFT)
>  	msr	mdcr_el2, x0
>  
>  	// Transfer the MM state from EL1 to EL2
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index dbc890511631..7b16f42d39f4 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -89,7 +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)
> + *  - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
>   *
>   * Additionally, KVM only traps guest accesses to the debug registers if
>   * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
> @@ -107,8 +107,8 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>  	trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
>  
>  	/*
> -	 * This also clears MDCR_EL2_E2PB_MASK to disable guest access
> -	 * to the profiling buffer.
> +	 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
> +	 * to disable guest access to the profiling and trace buffers
>  	 */
>  	vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
>  	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> index f401724f12ef..9499e18dd28f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> @@ -58,10 +58,51 @@ static void __debug_restore_spe(u64 pmscr_el1)
>  	write_sysreg_s(pmscr_el1, SYS_PMSCR_EL1);
>  }
>  
> +static void __debug_save_trace(u64 *trfcr_el1)
> +{
> +
> +	*trfcr_el1 = 0;
> +
> +	/* Check if we have TRBE */
> +	if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
> +						  ID_AA64DFR0_TRBE_SHIFT))
> +		return;
> +
> +	/* Check we can access the TRBE */
> +	if ((read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_PROG))
> +		return;
> +
> +	/* Check if the TRBE is enabled */
> +	if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_ENABLE))
> +		return;
> +	/*
> +	 * Prohibit trace generation while we are in guest.
> +	 * Since access to TRFCR_EL1 is trapped, the guest can't
> +	 * modify the filtering set by the host.
> +	 */
> +	*trfcr_el1 = read_sysreg_s(SYS_TRFCR_EL1);
> +	write_sysreg_s(0, SYS_TRFCR_EL1);
> +	isb();
> +	/* Drain the trace buffer to memory */
> +	tsb_csync();
> +	dsb(nsh);
> +}
> +
> +static void __debug_restore_trace(u64 trfcr_el1)
> +{
> +	if (!trfcr_el1)
> +		return;
> +
> +	/* Restore trace filter controls */
> +	write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1);
> +}
> +
>  void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
>  {
>  	/* Disable and flush SPE data generation */
>  	__debug_save_spe(&vcpu->arch.host_debug_state.pmscr_el1);
> +	/* Disable and flush Self-Hosted Trace generation */
> +	__debug_save_trace(&vcpu->arch.host_debug_state.trfcr_el1);
>  }
>  
>  void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> @@ -72,6 +113,7 @@ void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
>  void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
>  {
>  	__debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
> +	__debug_restore_trace(vcpu->arch.host_debug_state.trfcr_el1);
>  }
>  
>  void __debug_switch_to_host(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 68ab6b4d5141..736805232521 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -95,6 +95,7 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
>  
>  	mdcr_el2 &= MDCR_EL2_HPMN_MASK;
>  	mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
> +	mdcr_el2 |= MDCR_EL2_E2TB_MASK << MDCR_EL2_E2TB_SHIFT;
>  
>  	write_sysreg(mdcr_el2, mdcr_el2);
>  	if (is_protected_kvm_enabled())
> -- 
> 2.24.1
>