On 14/09/16 16:20, Vladimir Murzin wrote:
> On 13/09/16 10:22, Christoffer Dall wrote:
>> On Tue, Sep 13, 2016 at 10:11:10AM +0100, Marc Zyngier wrote:
>>> On 13/09/16 09:20, Christoffer Dall wrote:
>>>> 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.
>>>
>>> We could always revert the "likelihood" of that test once GICv3 has
>>> conquered the world. Or start patching the 32bit kernel like we do for
>>> 64bit...
>>>
>>>>
>>>>> + __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?
>>>
>>> Grepping through the tree shows that we're not the only abusers of this
>>> (dynamic debug is far worse!). Happy to write the additional macros and
>>> submit them if nobody beats me to it.
>>>
>>>>
>>>>
>>>>> };
>>>>>
>>>>> 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.
>>>
>>> Indeed, we should get this sorted, though I'm not sure this should be a
>>> blocker for this code.
>>>
>> Agreed, let's ship it!
>
> To make it clear, should I respin with "enabled" into the info message
> and macros for static keys?
I think we can fix the message up when applying the patches. As for the
macros, we should have a separate series that does it treewide.
Christoffer?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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