| Message ID | 20181017164210.16094-1-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kvm: arm64: fix caching of host MDCR_EL2 value | expand |
On 17/10/18 17:42, Mark Rutland wrote: > At boot time, KVM stashes the host MDCR_EL2 value, but only does this > when the kernel is not running in hyp mode (i.e. is non-VHE). In these > cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can > lead to CONSTRAINED UNPREDICTABLE behaviour. > > Since we use this value to derive the MDCR_EL2 value when switching > to/from a guest, after a guest have been run, the performance counters > do not behave as expected. This has been observed to result in accesses > via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant > counters, resulting in events not being counted. In these cases, only > the fixed-purpose cycle counter appears to work as expected. > > Fix this by always stashing the host MDCR_EL2 value, regardless of VHE. > > Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP") > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Christopher Dall <christoffer.dall@arm.com> > Cc: James Morse <james.morse@arm.com> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > Cc: kvmarm@lists.cs.columbia.edu > --- > virt/kvm/arm/arm.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index c92053bc3f96..8fb31a7cc22c 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy) > > __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr); > __cpu_init_stage2(); > - > - kvm_arm_init_debug(); > } > > static void cpu_hyp_reset(void) > @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void) > cpu_init_hyp_mode(NULL); > } > > + kvm_arm_init_debug(); > + > if (vgic_present) > kvm_vgic_init_cpu_hardware(); > } > Urghh. Lovely. Thanks for tracking that one down. I'll queue it immediately, with a Cc to stable. Thanks, M.
On 17/10/18 17:42, Mark Rutland wrote: > At boot time, KVM stashes the host MDCR_EL2 value, but only does this > when the kernel is not running in hyp mode (i.e. is non-VHE). In these > cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can > lead to CONSTRAINED UNPREDICTABLE behaviour. > > Since we use this value to derive the MDCR_EL2 value when switching > to/from a guest, after a guest have been run, the performance counters > do not behave as expected. This has been observed to result in accesses > via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant > counters, resulting in events not being counted. In these cases, only > the fixed-purpose cycle counter appears to work as expected. > > Fix this by always stashing the host MDCR_EL2 value, regardless of VHE. FWIW, Tested-by: Robin Murphy <robin.murphy@arm.com> > Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP") > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Christopher Dall <christoffer.dall@arm.com> > Cc: James Morse <james.morse@arm.com> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > Cc: kvmarm@lists.cs.columbia.edu > --- > virt/kvm/arm/arm.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index c92053bc3f96..8fb31a7cc22c 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy) > > __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr); > __cpu_init_stage2(); > - > - kvm_arm_init_debug(); > } > > static void cpu_hyp_reset(void) > @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void) > cpu_init_hyp_mode(NULL); > } > > + kvm_arm_init_debug(); > + > if (vgic_present) > kvm_vgic_init_cpu_hardware(); > } >
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index c92053bc3f96..8fb31a7cc22c 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy) __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr); __cpu_init_stage2(); - - kvm_arm_init_debug(); } static void cpu_hyp_reset(void) @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void) cpu_init_hyp_mode(NULL); } + kvm_arm_init_debug(); + if (vgic_present) kvm_vgic_init_cpu_hardware(); }
At boot time, KVM stashes the host MDCR_EL2 value, but only does this when the kernel is not running in hyp mode (i.e. is non-VHE). In these cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can lead to CONSTRAINED UNPREDICTABLE behaviour. Since we use this value to derive the MDCR_EL2 value when switching to/from a guest, after a guest have been run, the performance counters do not behave as expected. This has been observed to result in accesses via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant counters, resulting in events not being counted. In these cases, only the fixed-purpose cycle counter appears to work as expected. Fix this by always stashing the host MDCR_EL2 value, regardless of VHE. Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Christopher Dall <christoffer.dall@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: kvmarm@lists.cs.columbia.edu --- virt/kvm/arm/arm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)