| Message ID | 20181105143617.120602-4-marc.zyngier@arm.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | Workaround for Cortex-A76 erratum 1165522 | expand |
On Mon, Nov 05, 2018 at 02:36:15PM +0000, Marc Zyngier wrote: > It is a bit odd that we only install stage-2 translation after having > cleared HCR_EL2.TGE, which means that there is a window during which > AT requests could fail as stage-2 is not configured yet. > > Let's move stage-2 configuration before we clear TGE, making the > guest entry sequence clearer: we first configure all the guest stuff, > then only switch to the guest translation regime. > > Non-VHE doesn't have that kind of behaviour, and is left alone. I'm a bit confused about this statement. You can still issue a S12E1x AT instruction after activating traps (setting HCR_EL2.VM) on non-VHE and get at the same behavior, right? Is the point here that we are not aware of any non-VHE implementations that speculate AT instructions in this window, or am I missing some architectural nugget that prevents problems on non-VHE systems? In any case, why not change the non-VHE code as well to preserve symmetry for both types of systems? Thanks, Christoffer > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > --- > arch/arm64/kvm/hyp/switch.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c > index 7cc175c88a37..51d5d966d9e5 100644 > --- a/arch/arm64/kvm/hyp/switch.c > +++ b/arch/arm64/kvm/hyp/switch.c > @@ -499,8 +499,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu) > > sysreg_save_host_state_vhe(host_ctxt); > > - __activate_traps(vcpu); > __activate_vm(vcpu->kvm); > + __activate_traps(vcpu); > > sysreg_restore_guest_state_vhe(guest_ctxt); > __debug_switch_to_guest(vcpu); > -- > 2.19.1 >
On 06/11/18 08:06, Christoffer Dall wrote: > On Mon, Nov 05, 2018 at 02:36:15PM +0000, Marc Zyngier wrote: >> It is a bit odd that we only install stage-2 translation after having >> cleared HCR_EL2.TGE, which means that there is a window during which >> AT requests could fail as stage-2 is not configured yet. >> >> Let's move stage-2 configuration before we clear TGE, making the >> guest entry sequence clearer: we first configure all the guest stuff, >> then only switch to the guest translation regime. >> >> Non-VHE doesn't have that kind of behaviour, and is left alone. > > I'm a bit confused about this statement. You can still issue a S12E1x > AT instruction after activating traps (setting HCR_EL2.VM) on non-VHE > and get at the same behavior, right? > > Is the point here that we are not aware of any non-VHE implementations > that speculate AT instructions in this window, or am I missing some > architectural nugget that prevents problems on non-VHE systems? You're right. This is not an issue on non-VHE so far because we don't know of any such system that is broken in such a way (speculative AT instruction leading to inconsistent TLBs). > In any case, why not change the non-VHE code as well to preserve > symmetry for both types of systems? Happy to change that too. Thanks, M.
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c index 7cc175c88a37..51d5d966d9e5 100644 --- a/arch/arm64/kvm/hyp/switch.c +++ b/arch/arm64/kvm/hyp/switch.c @@ -499,8 +499,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu) sysreg_save_host_state_vhe(host_ctxt); - __activate_traps(vcpu); __activate_vm(vcpu->kvm); + __activate_traps(vcpu); sysreg_restore_guest_state_vhe(guest_ctxt); __debug_switch_to_guest(vcpu);
It is a bit odd that we only install stage-2 translation after having cleared HCR_EL2.TGE, which means that there is a window during which AT requests could fail as stage-2 is not configured yet. Let's move stage-2 configuration before we clear TGE, making the guest entry sequence clearer: we first configure all the guest stuff, then only switch to the guest translation regime. Non-VHE doesn't have that kind of behaviour, and is left alone. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> --- arch/arm64/kvm/hyp/switch.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)