From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9E7BE1FF5E6 for ; Mon, 3 Feb 2025 09:16:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738574190; cv=none; b=fWvMR803LQNJc1mchVfPkX2aohpSVZVDRPNRgVbDXt8Rp2ARNRiA6WaauyxbgDHM9galmnJhgLDCI1zLsqugotVtEuof4fHm09mA6vWSrATBlqlyqrwhM696W8Jl4GU+Xp05g/oJSYEsMbQsmccgWKAMZQwi6TPhQ6vJIG4ztd8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738574190; c=relaxed/simple; bh=DS5SYzVVo+ChyXQZP83o/2DRjTD9rsAZPhtrU7UImQQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iCNiD+Ifecy9pIZq1JaZSmi2J1Doz0A7CaRsGuXGU84nUDgeD1uuuVo5VZnIeCLG7bIkU6yRpiZFcsFrFmeWdJFqnf8LGfyBjJqJXK+1xC5iRU5K6LlWBy7pPMo/ZskpRHFy9FT7rVo74QM/R1d3tiZGzPRX/9nC9R91TpbRKXs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4A2611063; Mon, 3 Feb 2025 01:16:51 -0800 (PST) Received: from [10.162.16.79] (unknown [10.162.16.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 78A813F5A1; Mon, 3 Feb 2025 01:16:22 -0800 (PST) Message-ID: <533b2899-8805-4e57-afc2-d92ffeba6a7b@arm.com> Date: Mon, 3 Feb 2025 14:46:19 +0530 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v19 10/11] KVM: arm64: nvhe: Disable branch generation in nVHE guests To: "Rob Herring (Arm)" , Will Deacon , Mark Rutland , Catalin Marinas , Jonathan Corbet , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , James Clark Cc: linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev References: <20250202-arm-brbe-v19-v19-0-1c1300802385@kernel.org> <20250202-arm-brbe-v19-v19-10-1c1300802385@kernel.org> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20250202-arm-brbe-v19-v19-10-1c1300802385@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/3/25 06:13, Rob Herring (Arm) wrote: > From: Anshuman Khandual > > While BRBE can record branches within guests, the host recording > branches in guests is not supported by perf. Therefore, BRBE needs to be > disabled on guest entry and restored on exit. > > For nVHE, this requires explicit handling for guests. Before > entering a guest, save the BRBE state and disable the it. When > returning to the host, restore the state. > > For VHE, it is not necessary. We initialize > BRBCR_EL1.{E1BRE,E0BRE}=={0,0} at boot time, and HCR_EL2.TGE==1 while > running in the host. We configure BRBCR_EL2.{E2BRE,E0HBRE} to enable > branch recording in the host. When entering the guest, we set > HCR_EL2.TGE==0 which means BRBCR_EL1 is used instead of BRBCR_EL2. > Consequently for VHE, BRBE recording is disabled at EL1 and EL0 when > running a guest. > > Should recording in guests (by the host) ever be desired, the perf ABI > will need to be extended to distinguish guest addresses (struct > perf_branch_entry.priv) for starters. BRBE records would also need to be > invalidated on guest entry/exit as guest/host EL1 and EL0 records can't > be distinguished. > > Signed-off-by: Anshuman Khandual > Signed-off-by: Mark Rutland > Co-developed-by: Rob Herring (Arm) > Signed-off-by: Rob Herring (Arm) > --- > v19: > - Rework due to v6.14 debug flag changes > - Redo commit message > --- > arch/arm64/include/asm/kvm_host.h | 2 ++ > arch/arm64/kvm/debug.c | 4 ++++ > arch/arm64/kvm/hyp/nvhe/debug-sr.c | 32 ++++++++++++++++++++++++++++++++ > 3 files changed, 38 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 7cfa024de4e3..4fc246a1ee6b 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -619,6 +619,7 @@ struct kvm_host_data { > #define KVM_HOST_DATA_FLAG_HOST_SME_ENABLED 3 > #define KVM_HOST_DATA_FLAG_TRBE_ENABLED 4 > #define KVM_HOST_DATA_FLAG_EL1_TRACING_CONFIGURED 5 > +#define KVM_HOST_DATA_FLAG_HAS_BRBE 6 Although there is some variation in these feature names above, but seems like KVM_HOST_DATA_FLAG_HAS_BRBE is an appropriate one for BRBE handling. > unsigned long flags; > > struct kvm_cpu_context host_ctxt; > @@ -662,6 +663,7 @@ struct kvm_host_data { > u64 trfcr_el1; > /* Values of trap registers for the host before guest entry. */ > u64 mdcr_el2; > + u64 brbcr_el1; > } host_debug_state; > > /* Guest trace filter value */ > diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c > index 0e4c805e7e89..bc6015108a68 100644 > --- a/arch/arm64/kvm/debug.c > +++ b/arch/arm64/kvm/debug.c > @@ -81,6 +81,10 @@ void kvm_init_host_debug_data(void) > !(read_sysreg_s(SYS_PMBIDR_EL1) & PMBIDR_EL1_P)) > host_data_set_flag(HAS_SPE); > > + /* Check if we have BRBE implemented and available at the host */ > + if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_BRBE_SHIFT)) > + host_data_set_flag(HAS_BRBE); > + > if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceFilt_SHIFT)) { > /* Force disable trace in protected mode in case of no TRBE */ > if (is_protected_kvm_enabled()) > diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > index 2f4a4f5036bb..2a1c0f49792b 100644 > --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c > +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > @@ -92,12 +92,42 @@ static void __trace_switch_to_host(void) > *host_data_ptr(host_debug_state.trfcr_el1)); > } > > +static void __debug_save_brbe(u64 *brbcr_el1) > +{ > + *brbcr_el1 = 0; > + > + /* Check if the BRBE is enabled */ > + if (!(read_sysreg_el1(SYS_BRBCR) & (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_el1(SYS_BRBCR); > + write_sysreg_el1(0, SYS_BRBCR); > +} > + > +static void __debug_restore_brbe(u64 brbcr_el1) > +{ > + if (!brbcr_el1) > + return; > + > + /* Restore BRBE controls */ > + write_sysreg_el1(brbcr_el1, SYS_BRBCR); > +} > + > void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu) > { > /* Disable and flush SPE data generation */ > if (host_data_test_flag(HAS_SPE)) > __debug_save_spe(host_data_ptr(host_debug_state.pmscr_el1)); > > + /* Disable BRBE branch records */ > + if (host_data_test_flag(HAS_BRBE)) > + __debug_save_brbe(host_data_ptr(host_debug_state.brbcr_el1)); > + > if (__trace_needs_switch()) > __trace_switch_to_guest(); > } > @@ -111,6 +141,8 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu) > { > if (host_data_test_flag(HAS_SPE)) > __debug_restore_spe(*host_data_ptr(host_debug_state.pmscr_el1)); > + if (host_data_test_flag(HAS_BRBE)) > + __debug_restore_brbe(*host_data_ptr(host_debug_state.brbcr_el1)); > if (__trace_needs_switch()) > __trace_switch_to_host(); > } > LGTM