From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1214EEAD8; Mon, 4 Dec 2023 08:42:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="J0JS+DS0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75A2BC433C8; Mon, 4 Dec 2023 08:42:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701679370; bh=2hI21E5d7yISQiEU7qyNrku3/qKcokHOmhNwgh0+Zzk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=J0JS+DS0T/xYERSJvf7SVSu3t8FBddNgtC8ZdvbhLYQGdcePXwU5pma2oVAZQuGNN YB0JTppJ0yo50otMkg0tCS+dofexu50Gu4WLrsnNhvRgxDNCFztSRrG3IrU4me8GPb EWRKQR9pukbBtu1lwKtj/u0i1vxVjMgf6QDqwXK8w0xxFhhixUmNHUZ4gnLkznt1ny R8xed3hXpLbYtFXyh95K7BEefzRIeheVXR/3Y24tPLoc44+ODZSFQ84Y1f4Py3rpb3 x/EGmonseney/DAi0d4AN1VZhJLSeyM01YksyRDpYa0bHpvY4VPc3P/ZlGCdInfC/c U5urf+24tTnzQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1rA4XP-001962-VH; Mon, 04 Dec 2023 08:42:48 +0000 Date: Mon, 04 Dec 2023 08:42:47 +0000 Message-ID: <86ttoybbp4.wl-maz@kernel.org> From: Marc Zyngier To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Mark Brown , James Clark , Rob Herring , Suzuki Poulose , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , linux-perf-users@vger.kernel.org, Oliver Upton , James Morse , kvmarm@lists.linux.dev Subject: Re: [PATCH V15 5/8] KVM: arm64: nvhe: Disable branch generation in nVHE guests In-Reply-To: <20231201053906.1261704-6-anshuman.khandual@arm.com> References: <20231201053906.1261704-1-anshuman.khandual@arm.com> <20231201053906.1261704-6-anshuman.khandual@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, broonie@kernel.org, james.clark@arm.com, robh@kernel.org, suzuki.poulose@arm.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, linux-perf-users@vger.kernel.org, oliver.upton@linux.dev, james.morse@arm.com, kvmarm@lists.linux.dev X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Fri, 01 Dec 2023 05:39:03 +0000, 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 is just to avoid capturing records > in the guest kernel/userspace, which would be confusing the samples. Why does it have to be limited to non-VHE? What protects host EL0 records from guest's EL0 execution when the host is VHE? > > Cc: Marc Zyngier > Cc: Oliver Upton > Cc: James Morse > Cc: Suzuki K Poulose > Cc: Catalin Marinas > Cc: Will Deacon > Cc: kvmarm@lists.linux.dev > Cc: linux-arm-kernel@lists.infradead.org > CC: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > Changes in V15: > > - Dropped runtime BRBE enable for setting DEBUG_STATE_SAVE_BRBE > - Dropped BRBFCR_EL1 from __debug_save_brbe()/__debug_restore_brbe() > - Always save the live SYS_BRBCR_EL1 in host context and then check if > BRBE was enabled before resetting SYS_BRBCR_EL1 for the host > > arch/arm64/include/asm/kvm_host.h | 4 ++++ > arch/arm64/kvm/debug.c | 5 +++++ > arch/arm64/kvm/hyp/nvhe/debug-sr.c | 33 ++++++++++++++++++++++++++++++ > 3 files changed, 42 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 68421c74283a..1faa0430d8dd 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -449,6 +449,8 @@ enum vcpu_sysreg { > CNTHV_CVAL_EL2, > PMSCR_EL1, /* Statistical profiling extension */ > TRFCR_EL1, /* Self-hosted trace filters */ > + BRBCR_EL1, /* Branch Record Buffer Control Register */ > + BRBFCR_EL1, /* Branch Record Buffer Function Control Register */ Whose state is this? If this is limited to the host, it has no purpose in this enum. Once you add guest support, then it will make sense. > > NR_SYS_REGS /* Nothing after this line! */ > }; > @@ -753,6 +755,8 @@ struct kvm_vcpu_arch { > #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)) > +/* Save BRBE context if active */ > +#define DEBUG_STATE_SAVE_BRBE __vcpu_single_flag(iflags, BIT(9)) > > /* 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 2ab41b954512..fa46a70a9503 100644 > --- a/arch/arm64/kvm/debug.c > +++ b/arch/arm64/kvm/debug.c > @@ -354,6 +354,10 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu) > !(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) > @@ -361,6 +365,7 @@ 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); > + vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_BRBE); > } > > void kvm_etm_set_guest_trfcr(u64 trfcr_guest) > diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > index 6174f710948e..1994fc48b57c 100644 > --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c > +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > @@ -93,6 +93,33 @@ static void __debug_restore_trace(struct kvm_cpu_context *host_ctxt, > write_sysreg_s(ctxt_sys_reg(host_ctxt, TRFCR_EL1), SYS_TRFCR_EL1); > } > > +static void __debug_save_brbe(struct kvm_cpu_context *host_ctxt) > +{ > + ctxt_sys_reg(host_ctxt, BRBCR_EL1) = read_sysreg_s(SYS_BRBCR_EL1); > + > + /* Check if the BRBE is enabled */ > + if (!(ctxt_sys_reg(host_ctxt, BRBCR_EL1) & (BRBCR_ELx_E0BRE | BRBCR_ELx_ExBRE))) > + return; Why save BRBCR_EL1 if there is nothing enabled? It isn't like it can change behind your back, can it? > + > + /* > + * 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. > + */ > + write_sysreg_s(0, SYS_BRBCR_EL1); > + isb(); What is the point of this ISB? We're at EL2, and this only affects EL1. > +} > + > +static void __debug_restore_brbe(struct kvm_cpu_context *host_ctxt) > +{ > + if (!ctxt_sys_reg(host_ctxt, BRBCR_EL1)) > + return; So on one side you're using a flag, and on the other you're using the *value*. You need some consistency. > + > + /* Restore BRBE controls */ > + write_sysreg_s(ctxt_sys_reg(host_ctxt, BRBCR_EL1), SYS_BRBCR_EL1); > + isb(); Same question. > +} > + > void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt, > struct kvm_cpu_context *guest_ctxt) > { > @@ -102,6 +129,10 @@ void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt, > > if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRFCR)) > __debug_save_trace(host_ctxt, guest_ctxt); > + > + /* Disable BRBE branch records */ > + if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_BRBE)) > + __debug_save_brbe(host_ctxt); > } > > void __debug_switch_to_guest(struct kvm_vcpu *vcpu) > @@ -116,6 +147,8 @@ void __debug_restore_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt, > __debug_restore_spe(host_ctxt); > if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRFCR)) > __debug_restore_trace(host_ctxt, guest_ctxt); > + if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_BRBE)) > + __debug_restore_brbe(host_ctxt); > } > > void __debug_switch_to_host(struct kvm_vcpu *vcpu) The lifetime of this flag seems bogus, specially when there is nothing to do, which will always be the arch-majority of the executions. M. -- Without deviation from the norm, progress is not possible.