On Mon, Sep 12, 2016 at 03:49:15PM +0100, Vladimir Murzin wrote:
> Currently GIC backend is selected via alternative framework and this
> is fine. We are going to introduce vgic-v3 to 32-bit world and there
> we don't have patching framework in hand, so we can either check
> support for GICv3 every time we need to choose which backend to use or
> try to optimise it by using static keys. The later looks quite
> promising because we can share logic involved in selecting GIC backend
> between architectures if both uses static keys.
>
> This patch moves arm64 from alternative to static keys framework for
> selecting GIC backend. For that we embed static key into vgic_global
> and enable the key during vgic initialisation based on what has
> already been exposed by the host GIC driver.
>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
> ---
> arch/arm64/kvm/hyp/switch.c | 21 +++++++++++----------
> include/kvm/arm_vgic.h | 4 ++++
> virt/kvm/arm/vgic/vgic-init.c | 4 ++++
> virt/kvm/arm/vgic/vgic.c | 2 +-
> 4 files changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 5a84b45..d5c4cc5 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -16,6 +16,8 @@
> */
>
> #include <linux/types.h>
> +#include <linux/jump_label.h>
> +
> #include <asm/kvm_asm.h>
> #include <asm/kvm_hyp.h>
>
> @@ -126,17 +128,13 @@ static void __hyp_text __deactivate_vm(struct kvm_vcpu *vcpu)
> write_sysreg(0, vttbr_el2);
> }
>
> -static hyp_alternate_select(__vgic_call_save_state,
> - __vgic_v2_save_state, __vgic_v3_save_state,
> - ARM64_HAS_SYSREG_GIC_CPUIF);
> -
> -static hyp_alternate_select(__vgic_call_restore_state,
> - __vgic_v2_restore_state, __vgic_v3_restore_state,
> - ARM64_HAS_SYSREG_GIC_CPUIF);
> -
> static void __hyp_text __vgic_save_state(struct kvm_vcpu *vcpu)
> {
> - __vgic_call_save_state()(vcpu);
> + if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
It's a bit weird that we use _unlikely for GICv3 (at least if/when GICv3
hardware becomes mainstream), but as we don't have another primitive for
the 'default disabled' case, I suppose that's the best we can do.
> + __vgic_v3_save_state(vcpu);
> + else
> + __vgic_v2_save_state(vcpu);
> +
> write_sysreg(read_sysreg(hcr_el2) & ~HCR_INT_OVERRIDE, hcr_el2);
> }
>
> @@ -149,7 +147,10 @@ static void __hyp_text __vgic_restore_state(struct kvm_vcpu *vcpu)
> val |= vcpu->arch.irq_lines;
> write_sysreg(val, hcr_el2);
>
> - __vgic_call_restore_state()(vcpu);
> + if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> + __vgic_v3_restore_state(vcpu);
> + else
> + __vgic_v2_restore_state(vcpu);
> }
>
> static bool __hyp_text __true_value(void)
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 19b698e..994665a 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -23,6 +23,7 @@
> #include <linux/types.h>
> #include <kvm/iodev.h>
> #include <linux/list.h>
> +#include <linux/jump_label.h>
>
> #define VGIC_V3_MAX_CPUS 255
> #define VGIC_V2_MAX_CPUS 8
> @@ -63,6 +64,9 @@ struct vgic_global {
>
> /* Only needed for the legacy KVM_CREATE_IRQCHIP */
> bool can_emulate_gicv2;
> +
> + /* GIC system register CPU interface */
> + struct static_key_false gicv3_cpuif;
Documentation/static-keys.txt says that we are not supposed to use
struct static_key_false directly. This will obviously work quite
nicely, but we could consider adding a pair of
DECLARE_STATIC_KEY_TRUE/FALSE macros that don't have the assignments,
but obviously this will need an ack from other maintainers.
Thoughts?
> };
>
> extern struct vgic_global kvm_vgic_global_state;
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index 83777c1..14d6718 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -405,6 +405,10 @@ int kvm_vgic_hyp_init(void)
> break;
> case GIC_V3:
> ret = vgic_v3_probe(gic_kvm_info);
> + if (!ret) {
> + static_branch_enable(&kvm_vgic_global_state.gicv3_cpuif);
> + kvm_info("GIC system register CPU interface\n");
nit: add enabled to the info message?
> + }
> break;
> default:
> ret = -ENODEV;
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index e83b7fe..8a529a7 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -29,7 +29,7 @@
> #define DEBUG_SPINLOCK_BUG_ON(p)
> #endif
>
> -struct vgic_global __section(.hyp.text) kvm_vgic_global_state;
> +struct vgic_global __section(.hyp.text) kvm_vgic_global_state = {.gicv3_cpuif = STATIC_KEY_FALSE_INIT,};
>
> /*
> * Locking order is always:
> --
> 1.7.9.5
>
Overall this looks really nice, as long as we're clear on the static
keys stuff.
Thanks!
-Christoffer
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