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();
}
Thanks,
-Christoffer
