Messages in this thread Patch in this message | | | Date | Thu, 29 Feb 2024 18:40:54 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH V16 5/8] KVM: arm64: nvhe: Disable branch generation in nVHE guests |
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On Thu, 25 Jan 2024 09:41:16 +0000, Anshuman Khandual <anshuman.khandual@arm.com> wrote: > > Disable the BRBE before we enter the guest, saving the status and enable it > back once we get out of the guest. This avoids capturing branch records in > the guest kernel or userspace, which would be confusing the host samples. > > Cc: Marc Zyngier <maz@kernel.org> > Cc: Oliver Upton <oliver.upton@linux.dev> > Cc: James Morse <james.morse@arm.com> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: kvmarm@lists.linux.dev > Cc: linux-arm-kernel@lists.infradead.org > CC: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > Changes in V16: > > - Dropped BRBCR_EL1 and BRBFCR_EL1 from enum vcpu_sysreg > - Reverted back the KVM NVHE patch - used host_debug_state based 'brbcr_el1' > element, and dropped the previous dependency on Jame's coresight series > > arch/arm64/include/asm/kvm_host.h | 5 ++++- > arch/arm64/kvm/debug.c | 5 +++++ > arch/arm64/kvm/hyp/nvhe/debug-sr.c | 33 ++++++++++++++++++++++++++++++ > 3 files changed, 42 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 21c57b812569..bce8792092af 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -569,7 +569,7 @@ struct kvm_vcpu_arch { > u8 cflags; > > /* Input flags to the hypervisor code, potentially cleared after use */ > - u8 iflags; > + u16 iflags; > > /* State flags for kernel bookkeeping, unused by the hypervisor code */ > u8 sflags; > @@ -610,6 +610,7 @@ struct kvm_vcpu_arch { > u64 pmscr_el1; > /* Self-hosted trace */ > u64 trfcr_el1; > + u64 brbcr_el1; > } host_debug_state; > > /* VGIC state */ > @@ -779,6 +780,8 @@ struct kvm_vcpu_arch { > #define DEBUG_STATE_SAVE_TRBE __vcpu_single_flag(iflags, BIT(6)) > /* vcpu running in HYP context */ > #define VCPU_HYP_CONTEXT __vcpu_single_flag(iflags, BIT(7)) > +/* Save BRBE context if active */ > +#define DEBUG_STATE_SAVE_BRBE __vcpu_single_flag(iflags, BIT(8)) > > /* 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 8725291cb00a..99f85d8acbf3 100644 > --- a/arch/arm64/kvm/debug.c > +++ b/arch/arm64/kvm/debug.c > @@ -335,10 +335,15 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu) > if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) && > !(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) > { > vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE); > vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE); > + vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_BRBE); > } > diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > index 4558c02eb352..79bcf0fb1326 100644 > --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c > +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > @@ -79,6 +79,34 @@ static void __debug_restore_trace(u64 trfcr_el1) > write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1); > } > > +static void __debug_save_brbe(u64 *brbcr_el1) > +{ > + *brbcr_el1 = 0; > + > + /* Check if the BRBE is enabled */ > + if (!(read_sysreg_s(SYS_BRBCR_EL1) & (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_s(SYS_BRBCR_EL1); > + write_sysreg_s(0, SYS_BRBCR_EL1);
As for TRFCR and PMSCR, this is broken on hVHE.
Please see [1]
M.
[1] https://lore.kernel.org/r/20240229145417.3606279-1-maz@kernel.org
-- Without deviation from the norm, progress is not possible.
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