Subject: [PATCH v3 1/8] arm64: KVM: Use static keys for selecting the GIC backend

From: [email-masked] (Marc Zyngier)
Date: Fri, 9 Sep 2016 10:19:35 +0100

Hi Vladimir,

On 08/09/16 17:06, 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. To make static keys work on hyp side we need to
> make sure that hyp can access to the key which is RW data. For that
> purpose introduce __hyp_data section we can map to hyp and place the
> key there.
> 
> Signed-off-by: Vladimir Murzin <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_host.h   |   13 +++++++++++++
>  arch/arm/include/asm/kvm_hyp.h    |    2 --
>  arch/arm/include/asm/virt.h       |    8 ++++++++
>  arch/arm/kernel/vmlinux.lds.S     |    6 ++++++
>  arch/arm/kvm/arm.c                |   19 +++++++++++++++++++
>  arch/arm64/include/asm/kvm_host.h |   15 +++++++++++++++
>  arch/arm64/include/asm/kvm_hyp.h  |    2 --
>  arch/arm64/include/asm/virt.h     |    7 +++++++
>  arch/arm64/kernel/vmlinux.lds.S   |    6 ++++++
>  arch/arm64/kvm/hyp/switch.c       |   19 +++++++++----------
>  10 files changed, 83 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index de338d9..bfa6eec 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -21,11 +21,14 @@
>  
>  #include <linux/types.h>
>  #include <linux/kvm_types.h>
> +#include <linux/jump_label.h>
> +
>  #include <asm/kvm.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_mmio.h>
>  #include <asm/fpstate.h>
>  #include <kvm/arm_arch_timer.h>
> +#include <asm/cputype.h>
>  
>  #define __KVM_HAVE_ARCH_INTC_INITIALIZED
>  
> @@ -310,4 +313,14 @@ static inline int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>  	return -ENXIO;
>  }
>  
> +extern struct static_key_false kvm_gicv3_cpuif;

I think we should follow the model set by kvm_vgic_global_state, which
is declared in arm_vgic.h. Even better, we should *embed* the static key
in this structure. This will reduce the clutter and we wouldn't have to
deal with all the section stuff (the hyp_data thing is a good cleanup,
but I'd like to see it as a separate patch if possible).

> +
> +static inline bool kvm_arm_support_gicv3_cpuif(void)
> +{
> +	if (IS_ENABLED(CONFIG_ARM_GIC_V3))
> +		return !!cpuid_feature_extract(CPUID_EXT_PFR1, 28);
> +	else
> +		return false;
> +}
> +
>  #endif /* __ARM_KVM_HOST_H__ */
> diff --git a/arch/arm/include/asm/kvm_hyp.h b/arch/arm/include/asm/kvm_hyp.h
> index 6eaff28..bd9434e 100644
> --- a/arch/arm/include/asm/kvm_hyp.h
> +++ b/arch/arm/include/asm/kvm_hyp.h
> @@ -23,8 +23,6 @@
>  #include <asm/kvm_mmu.h>
>  #include <asm/vfp.h>
>  
> -#define __hyp_text __section(.hyp.text) notrace
> -
>  #define __ACCESS_CP15(CRn, Op1, CRm, Op2)	\
>  	"mrc", "mcr", __stringify(p15, Op1, %0, CRn, CRm, Op2), u32
>  #define __ACCESS_CP15_64(Op1, CRm)		\
> diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
> index a2e75b8..e61a809 100644
> --- a/arch/arm/include/asm/virt.h
> +++ b/arch/arm/include/asm/virt.h
> @@ -28,6 +28,9 @@
>   */
>  #define BOOT_CPU_MODE_MISMATCH	PSR_N_BIT
>  
> +#define __hyp_text __section(.hyp.text) notrace
> +#define __hyp_data __section(.hyp.data)
> +
>  #ifndef __ASSEMBLY__
>  #include <asm/cacheflush.h>
>  
> @@ -87,6 +90,11 @@ extern char __hyp_idmap_text_end[];
>  /* The section containing the hypervisor text */
>  extern char __hyp_text_start[];
>  extern char __hyp_text_end[];
> +
> +/* The section containing the hypervisor data */
> +extern char __hyp_data_start[];
> +extern char __hyp_data_end[];
> +
>  #endif
>  
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index d24e5dd..6d53824 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -25,6 +25,11 @@
>  	*(.hyp.text)							\
>  	VMLINUX_SYMBOL(__hyp_text_end) = .;
>  
> +#define HYPERVISOR_DATA							\
> +	VMLINUX_SYMBOL(__hyp_data_start) = .;				\
> +	*(.hyp.data)							\
> +	VMLINUX_SYMBOL(__hyp_data_end) = .;
> +
>  #define IDMAP_TEXT							\
>  	ALIGN_FUNCTION();						\
>  	VMLINUX_SYMBOL(__idmap_text_start) = .;				\
> @@ -256,6 +261,7 @@ SECTIONS
>  		 */
>  		DATA_DATA
>  		CONSTRUCTORS
> +		HYPERVISOR_DATA

If you follow my idea of of embedding the static key, we can defer all
of this to another patch set.

>  
>  		_edata = .;
>  	}
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 75f130e..f966763 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -27,6 +27,7 @@
>  #include <linux/mman.h>
>  #include <linux/sched.h>
>  #include <linux/kvm.h>
> +#include <linux/irqchip/arm-gic-v3.h>
>  #include <trace/events/kvm.h>
>  #include <kvm/arm_pmu.h>
>  
> @@ -68,6 +69,9 @@ static bool vgic_present;
>  
>  static DEFINE_PER_CPU(unsigned char, kvm_arm_hardware_enabled);
>  
> +/* GIC system register CPU interface */
> +__hyp_data DEFINE_STATIC_KEY_FALSE(kvm_gicv3_cpuif);
> +
>  static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu)
>  {
>  	BUG_ON(preemptible());
> @@ -1178,6 +1182,14 @@ static int init_common_resources(void)
>  		return -ENOMEM;
>  	}
>  
> +	if (kvm_arm_support_gicv3_cpuif()) {

Why do we need to check this? If we identify a GICv3 (as exposed by the
host GIC driver), let's just use that.

> +		if (!gic_enable_sre())
> +			kvm_info("GIC CPU interface present but disabled by higher exception level\n");

Do you really want to try and enable SRE there? It feels wrong, as it
will already have been enabled by the host driver. Also, we don't
support having GICv3 in a non-SRE configuration (firmware must expose a
GICv2 in that case).

> +
> +		static_branch_enable(&kvm_gicv3_cpuif);
> +		kvm_info("GIC system register CPU interface\n");
> +	}

Can this whole hunk be moved to the vgic initialization instead?

> +
>  	return 0;
>  }
>  
> @@ -1297,6 +1309,13 @@ static int init_hyp_mode(void)
>  		goto out_err;
>  	}
>  
> +	err = create_hyp_mappings(kvm_ksym_ref(__hyp_data_start),
> +				  kvm_ksym_ref(__hyp_data_end), PAGE_HYP);
> +	if (err) {
> +		kvm_err("Cannot map hyp data section\n");
> +		goto out_err;
> +	}
> +
>  	err = create_hyp_mappings(kvm_ksym_ref(__start_rodata),
>  				  kvm_ksym_ref(__end_rodata), PAGE_HYP_RO);
>  	if (err) {
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3eda975..1da74e8 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -24,6 +24,9 @@
>  
>  #include <linux/types.h>
>  #include <linux/kvm_types.h>
> +#include <linux/jump_label.h>
> +
> +#include <asm/cpufeature.h>
>  #include <asm/kvm.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_mmio.h>
> @@ -390,4 +393,16 @@ static inline void __cpu_init_stage2(void)
>  		  "PARange is %d bits, unsupported configuration!", parange);
>  }
>  
> +extern struct static_key_false kvm_gicv3_cpuif;
> +
> +static inline bool kvm_arm_support_gicv3_cpuif(void)
> +{
> +	int reg = read_system_reg(SYS_ID_AA64PFR0_EL1);
> +
> +	if (IS_ENABLED(CONFIG_ARM_GIC_V3))
> +		return !!cpuid_feature_extract_unsigned_field(reg, ID_AA64PFR0_GIC_SHIFT);
> +
> +	return false;
> +}
> +
>  #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index cff5105..5c4ac82 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -23,8 +23,6 @@
>  #include <asm/kvm_mmu.h>
>  #include <asm/sysreg.h>
>  
> -#define __hyp_text __section(.hyp.text) notrace
> -
>  #define read_sysreg_elx(r,nvh,vh)					\
>  	({								\
>  		u64 reg;						\
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 1788545..c49426e 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -42,6 +42,9 @@
>  #define BOOT_CPU_MODE_EL1	(0xe11)
>  #define BOOT_CPU_MODE_EL2	(0xe12)
>  
> +#define __hyp_text __section(.hyp.text) notrace
> +#define __hyp_data __section(.hyp.data)
> +
>  #ifndef __ASSEMBLY__
>  
>  #include <asm/ptrace.h>
> @@ -95,6 +98,10 @@ extern char __hyp_idmap_text_end[];
>  extern char __hyp_text_start[];
>  extern char __hyp_text_end[];
>  
> +/* The section containing the hypervisor data */
> +extern char __hyp_data_start[];
> +extern char __hyp_data_end[];
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* ! __ASM__VIRT_H */
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 659963d..ea94a10 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -40,6 +40,11 @@ jiffies = jiffies_64;
>  	*(.hyp.text)					\
>  	VMLINUX_SYMBOL(__hyp_text_end) = .;
>  
> +#define HYPERVISOR_DATA					\
> +	VMLINUX_SYMBOL(__hyp_data_start) = .;		\
> +	.hyp.data : {*(.hyp.data)}			\
> +	VMLINUX_SYMBOL(__hyp_data_end) = .;
> +
>  #define IDMAP_TEXT					\
>  	. = ALIGN(SZ_4K);				\
>  	VMLINUX_SYMBOL(__idmap_text_start) = .;		\
> @@ -185,6 +190,7 @@ SECTIONS
>  	_data = .;
>  	_sdata = .;
>  	RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
> +	HYPERVISOR_DATA
>  	PECOFF_EDATA_PADDING
>  	_edata = .;
>  
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 5a84b45..cdc1360 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -126,17 +126,13 @@ 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_gicv3_cpuif))
> +		__vgic_v3_save_state(vcpu);
> +	else
> +		__vgic_v2_save_state(vcpu);
> +
>  	write_sysreg(read_sysreg(hcr_el2) & ~HCR_INT_OVERRIDE, hcr_el2);
>  }
>  
> @@ -149,7 +145,10 @@ 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_gicv3_cpuif))
> +		__vgic_v3_restore_state(vcpu);
> +	else
> +		__vgic_v2_restore_state(vcpu);
>  }
>  
>  static bool __hyp_text __true_value(void)
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...