Re: [PATCH v6 22/64] KVM: arm64: nv: Respect virtual HCR_EL2.TWX setting

Alexandru Elisei
2022-02-04T16:02:40Z

Hi,

On Fri, Feb 04, 2022 at 03:40:15PM +0000, Alexandru Elisei wrote:
> Hi Marc,
>
> On Fri, Jan 28, 2022 at 12:18:30PM +0000, Marc Zyngier wrote:
> > From: Jintack Lim <jintack.lim@linaro.org>
> >
> > Forward exceptions due to WFI or WFE instructions to the virtual EL2 if
> > they are not coming from the virtual EL2 and virtual HCR_EL2.TWX is set.
> >
> > Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> > arch/arm64/include/asm/kvm_nested.h | 2 ++
> > arch/arm64/kvm/Makefile | 2 +-
> > arch/arm64/kvm/handle_exit.c | 11 ++++++++++-
> > arch/arm64/kvm/nested.c | 28 ++++++++++++++++++++++++++++
> > 4 files changed, 41 insertions(+), 2 deletions(-)
> > create mode 100644 arch/arm64/kvm/nested.c
> >
> > diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> > index 5a85be6d8eb3..79d382fa02ea 100644
> > --- a/arch/arm64/include/asm/kvm_nested.h
> > +++ b/arch/arm64/include/asm/kvm_nested.h
> > @@ -65,4 +65,6 @@ static inline u64 translate_cnthctl_el2_to_cntkctl_el1(u64 cnthctl)
> > (cnthctl & (CNTHCTL_EVNTI | CNTHCTL_EVNTDIR | CNTHCTL_EVNTEN)));
> > }
> >
> > +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
> > +
> > #endif /* __ARM64_KVM_NESTED_H */
> > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> > index b67c4ebd72b1..dbaf42ff65f1 100644
> > --- a/arch/arm64/kvm/Makefile
> > +++ b/arch/arm64/kvm/Makefile
> > @@ -14,7 +14,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
> > inject_fault.o va_layout.o handle_exit.o \
> > guest.o debug.o reset.o sys_regs.o \
> > vgic-sys-reg-v3.o fpsimd.o pmu.o pkvm.o \
> > - arch_timer.o trng.o emulate-nested.o \
> > + arch_timer.o trng.o emulate-nested.o nested.o \
> > vgic/vgic.o vgic/vgic-init.o \
> > vgic/vgic-irqfd.o vgic/vgic-v2.o \
> > vgic/vgic-v3.o vgic/vgic-v4.o \
> > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> > index 0cedef6e0d80..a1b1bbf3d598 100644
> > --- a/arch/arm64/kvm/handle_exit.c
> > +++ b/arch/arm64/kvm/handle_exit.c
> > @@ -119,7 +119,16 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu)
> > */
> > static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
> > {
> > - if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE) {
> > + bool is_wfe = !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE);
> > +
> > + if (vcpu_has_nv(vcpu)) {
> > + int ret = handle_wfx_nested(vcpu, is_wfe);
> > +
> > + if (ret != -EINVAL)
> > + return ret;
>
> I find this rather clunky. The common pattern is that a function returns
> early when it encounters an error, but here this pattern is reversed:
> -EINVAL means that handle_wfx_nested() failed in handling the WFx, so
> proceed as usual; conversly, anything but -EINVAL means handle_wfx_nested()
> was successful in handling WFx, so exit early from kvm_handle_wfx().
>
> That would be ok by itself, but if we dig deeper, handle_wfx_nested() ends up
> calling kvm_inject_nested(), where -EINVAL is actually an error code. Granted,
> that should never happen, because kvm_handle_wfx() first checks vcpu_has_nv(),
> but still feels like something that could be improved.
>
> Maybe changing handle_wfx_nested() like this would be better:
> [..]

Or change kvm_handle_wfx() to handle the WFx trap like kvm_handle_fpasimd():

if (guest_wfx_traps_enabled(vcpu))
return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));

Thanks,
Alex