On Thu, 22 Feb 2018 14:42:27 +0000,
Christoffer Dall wrote:
>
> On Thu, Feb 22, 2018 at 12:32:11PM +0000, Marc Zyngier wrote:
> > On 15/02/18 21:03, Christoffer Dall wrote:
> > > Just like we can program the GICv2 hypervisor control interface directly
> > > from the core vgic code, we can do the same for the GICv3 hypervisor
> > > control interface on VHE systems.
> > >
> > > We do this by simply calling the save/restore functions when we have VHE
> > > and we can then get rid of the save/restore function calls from the VHE
> > > world switch function.
> > >
> > > One caveat is that we now write GICv3 system register state before the
> > > potential early exit path in the run loop, and because we sync back
> > > state in the early exit path, we have to ensure that we read a
> > > consistent GIC state from the sync path, even though we have never
> > > actually run the guest with the newly written GIC state. We solve this
> > > by inserting an ISB in the early exit path.
> > >
> > > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> > > ---
> > >
> > > Notes:
> > > Changes since v2:
> > > - Added ISB in the early exit path in the run loop as explained
> > > in the commit message.
> > >
> > > arch/arm64/kvm/hyp/switch.c | 3 ---
> > > virt/kvm/arm/arm.c | 1 +
> > > virt/kvm/arm/vgic/vgic.c | 5 +++++
> > > 3 files changed, 6 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > > index cbafc27a617b..466cfcdbcaf3 100644
> > > --- a/arch/arm64/kvm/hyp/switch.c
> > > +++ b/arch/arm64/kvm/hyp/switch.c
> > > @@ -399,8 +399,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> > > __activate_traps(vcpu);
> > > __activate_vm(vcpu->kvm);
> > >
> > > - __vgic_restore_state(vcpu);
> > > -
> > > sysreg_restore_guest_state_vhe(guest_ctxt);
> > > __debug_switch_to_guest(vcpu);
> > >
> > > @@ -414,7 +412,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> > > fp_enabled = fpsimd_enabled_vhe();
> > >
> > > sysreg_save_guest_state_vhe(guest_ctxt);
> > > - __vgic_save_state(vcpu);
> > >
> > > __deactivate_traps(vcpu);
> > >
> > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > > index 5bd879c78951..6de7641f3ff2 100644
> > > --- a/virt/kvm/arm/arm.c
> > > +++ b/virt/kvm/arm/arm.c
> > > @@ -717,6 +717,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> > > if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
> > > kvm_request_pending(vcpu)) {
> > > vcpu->mode = OUTSIDE_GUEST_MODE;
> > > + isb(); /* Ensure work in x_flush_hwstate is committed */
> > > kvm_pmu_sync_hwstate(vcpu);
> > > if (static_branch_unlikely(&userspace_irqchip_in_use))
> > > kvm_timer_sync_hwstate(vcpu);
> > > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> > > index 12e2a28f437e..d0a19a8c196a 100644
> > > --- a/virt/kvm/arm/vgic/vgic.c
> > > +++ b/virt/kvm/arm/vgic/vgic.c
> > > @@ -19,6 +19,7 @@
> > > #include <linux/list_sort.h>
> > > #include <linux/interrupt.h>
> > > #include <linux/irq.h>
> > > +#include <asm/kvm_hyp.h>
> > >
> > > #include "vgic.h"
> > >
> > > @@ -753,6 +754,8 @@ static inline void vgic_save_state(struct kvm_vcpu *vcpu)
> > > {
> > > if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> > > vgic_v2_save_state(vcpu);
> > > + else if (has_vhe())
> > > + __vgic_v3_save_state(vcpu);
> > > }
> > >
> > > /* Sync back the hardware VGIC state into our emulation after a guest's run. */
> > > @@ -777,6 +780,8 @@ static inline void vgic_restore_state(struct kvm_vcpu *vcpu)
> > > {
> > > if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> > > vgic_v2_restore_state(vcpu);
> > > + else if (has_vhe())
> > > + __vgic_v3_restore_state(vcpu);
> > > }
> > >
> > > /* Flush our emulation state into the GIC hardware before entering the guest. */
> > >
> >
> > I'm slowly wrapping my brain around this thing again. If I grasp the
> > general idea, we end up with two cases:
> >
> > (1) The GIC is accessible from the kernel, and we save/restore it
> > outside of the HYP code.
> >
> > (2) The GIC is only accessible from the HYP code, and we do it there.
> >
> > Maybe we should bite the bullet and introduce that primitive instead?
> >
>
> You mean something the following?
>
> static inline bool can_access_vgic_from_kernel(void)
> {
> /*
> * GICv2 can always be accessed from the kernel because it is
> * memory-mapped, and VHE systems can access GICv3 EL2 system
> * registers.
> */
> return !static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) || has_vhe();
> }
Yes. I think this would go a long way in making this code easy to
understand. It also mean that we can have a unified save/restore
function that picks the right GIC back-end, resulting in less
code duplication.
Thoughts?
M.
--
Jazz is not dead, it just smell funny.
