Messages in this thread | | | Subject | Re: [PATCH v2 11/18] KVM: arm64: don't trap Statistical Profiling controls to EL2 | Date | Mon, 23 Dec 2019 12:05:12 +0000 | From | Marc Zyngier <> |
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On 2019-12-23 11:56, Andrew Murray wrote: > On Sun, Dec 22, 2019 at 10:42:05AM +0000, Marc Zyngier wrote: >> On Fri, 20 Dec 2019 14:30:18 +0000, >> Andrew Murray <andrew.murray@arm.com> wrote: >> > >> > As we now save/restore the profiler state there is no need to trap >> > accesses to the statistical profiling controls. Let's unset the >> > _TPMS bit. >> > >> > Signed-off-by: Andrew Murray <andrew.murray@arm.com> >> > --- >> > arch/arm64/kvm/debug.c | 2 -- >> > 1 file changed, 2 deletions(-) >> > >> > diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c >> > index 43487f035385..07ca783e7d9e 100644 >> > --- a/arch/arm64/kvm/debug.c >> > +++ b/arch/arm64/kvm/debug.c >> > @@ -88,7 +88,6 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu >> *vcpu) >> > * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR) >> > * - Debug ROM Address (MDCR_EL2_TDRA) >> > * - OS related registers (MDCR_EL2_TDOSA) >> > - * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB) >> > * >> > * Additionally, KVM only traps guest accesses to the debug >> registers if >> > * the guest is not actively using them (see the >> KVM_ARM64_DEBUG_DIRTY >> > @@ -111,7 +110,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu >> *vcpu) >> > */ >> > vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & >> MDCR_EL2_HPMN_MASK; >> > vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | >> > - MDCR_EL2_TPMS | >> >> No. This is an *optional* feature (the guest could not be presented >> with the SPE feature, or the the support simply not be compiled in). >> >> If the guest is not allowed to see the feature, for whichever >> reason, >> the traps *must* be enabled and handled. > > I'll update this (and similar) to trap such registers when we don't > support > SPE in the guest. > > My original concern in the cover letter was in how to prevent the > guest > from attempting to use these registers in the first place - I think > the > solution I was looking for is to trap-and-emulate ID_AA64DFR0_EL1 > such that > the PMSVer bits indicate that SPE is not emulated.
That, and active trapping of the SPE system registers resulting in injection of an UNDEF into the offending guest.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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