Messages in this thread | | | Subject | Re: [PATCH v5 07/19] arm64: kvm: Enable access to TRBE support for host | From | Suzuki K Poulose <> | Date | Tue, 30 Mar 2021 14:34:23 +0100 |
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On 30/03/2021 13:15, Marc Zyngier wrote: > On Tue, 30 Mar 2021 12:12:49 +0100, > Suzuki K Poulose <suzuki.poulose@arm.com> wrote: >> >> Hi Marc >> >> On 30/03/2021 11:12, Marc Zyngier wrote: >>> Hi Suzuki, >>> >>> [+ Alex] >>> >>> On Tue, 23 Mar 2021 12:06:35 +0000, >>> Suzuki K Poulose <suzuki.poulose@arm.com> 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@kernel.org> >>>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>>> Cc: Marc Zyngier <maz@kernel.org> >>>> Cc: Mark Rutland <mark.rutland@arm.com> >>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com> >>>> Acked-by: Mathieu Poirier <mathieu.poirier@linaro.org> >>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>> --- >>>> 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(-) >>>> >>>> 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)) >>> >>> Where are these bits defined? DDI0487G_a has them as RES0. >> >> They are part of the Future architecture technology and a register >> definition XML is available here : >> >> https://developer.arm.com/documentation/ddi0601/2020-12/AArch64-Registers/MDCR-EL2--Monitor-Debug-Configuration-Register--EL2-?lang=en#fieldset_0-25_24-1 >> > > It be worth adding a pointer to that documentation until this is part > of a released ARM ARM. > >>> >>>> #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) >>> >>> For the record, this is likely to conflict with [1], although that >>> patch still has some issues. >> >> Thanks for the heads up. I think that patch will also conflict with my >> fixes that is queued in kvmarm/fixes. > > Most probably. This is a popular landing spot, these days... > >> >> >>> >>>> * >>>> * 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) >>>> +{ >>>> + >>> >>> Spurious blank line? >>> >> >> Sure, will fix it >> >>>> + *trfcr_el1 = 0; >>>> + >>>> + /* Check if we have TRBE */ >>>> + if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1), >>>> + ID_AA64DFR0_TRBE_SHIFT)) >>>> + return; >>> >>> Do we have a way to track this that doesn't involve reading an ID >>> register? This is on the hot path, and is going to really suck badly >>> with NV (which traps all ID regs for obvious reasons). I would have >>> hoped that one way or another, we'd have a static key for this. >> >> TRBE, like SPE can be optionally enabled on a subset of the CPUs. We >> could have a per-CPU static key in the worst case. I guess this would >> apply to SPE as well. > > Ah, so you want to support asymmetric tracing... fair enough. But I > don't think you need a per-CPU static key (and I'm not sure how that'd > work either). You could have a static key indicating if *any* CPU > implements tracing, in which case the check only happens when at least > one CPU is capable of tracing. > > You would only need a new capability. > >> May be we could do this check at kvm_arch_vcpu_load()/put() ? > > That would extend the tracing blackout period enormously, wouldn't it? > I'm not sure that's the best thing to do...
Sorry for not making this clear. We could check if the SPE/TRBE is available on this CPU (including the PMB/TRB_IDR bits and a set a flag in the VCPU on every kvm_arch_vcpu_load() and cleared on put. The actual switching code could check this flag and check if the unit is enabled and then do the actual save/restore as we do below. (We may be able to even check if unit is enabled there, need to double check this.)
Cheers Suzuki
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