Subject: Re: [PATCH v2 12/18] KVM: arm64: add a new vcpu device control group for SPEv1

From: Marc Zyngier <[email-masked]>
Date: Sun, 22 Dec 2019 11:03:04 +0000

On Fri, 20 Dec 2019 14:30:19 +0000,
Andrew Murray <[email-masked]> wrote:
> 
> From: Sudeep Holla <[email-masked]>
> 
> To configure the virtual SPEv1 overflow interrupt number, we use the
> vcpu kvm_device ioctl, encapsulating the KVM_ARM_VCPU_SPE_V1_IRQ
> attribute within the KVM_ARM_VCPU_SPE_V1_CTRL group.
> 
> After configuring the SPEv1, call the vcpu ioctl with attribute
> KVM_ARM_VCPU_SPE_V1_INIT to initialize the SPEv1.
> 
> Signed-off-by: Sudeep Holla <[email-masked]>
> Signed-off-by: Andrew Murray <[email-masked]>
> ---
>  Documentation/virt/kvm/devices/vcpu.txt |  28 ++++
>  arch/arm64/include/asm/kvm_host.h       |   2 +-
>  arch/arm64/include/uapi/asm/kvm.h       |   4 +
>  arch/arm64/kvm/Makefile                 |   1 +
>  arch/arm64/kvm/guest.c                  |   6 +
>  arch/arm64/kvm/reset.c                  |   3 +
>  include/kvm/arm_spe.h                   |  45 +++++++
>  include/uapi/linux/kvm.h                |   1 +
>  virt/kvm/arm/arm.c                      |   1 +
>  virt/kvm/arm/spe.c                      | 163 ++++++++++++++++++++++++
>  10 files changed, 253 insertions(+), 1 deletion(-)
>  create mode 100644 virt/kvm/arm/spe.c
> 
> diff --git a/Documentation/virt/kvm/devices/vcpu.txt b/Documentation/virt/kvm/devices/vcpu.txt
> index 6f3bd64a05b0..cefad056d677 100644
> --- a/Documentation/virt/kvm/devices/vcpu.txt
> +++ b/Documentation/virt/kvm/devices/vcpu.txt
> @@ -74,3 +74,31 @@ Specifies the base address of the stolen time structure for this VCPU. The
>  base address must be 64 byte aligned and exist within a valid guest memory
>  region. See Documentation/virt/kvm/arm/pvtime.txt for more information
>  including the layout of the stolen time structure.
> +
> +4. GROUP: KVM_ARM_VCPU_SPE_V1_CTRL
> +Architectures: ARM64
> +
> +4.1. ATTRIBUTE: KVM_ARM_VCPU_SPE_V1_IRQ
> +Parameters: in kvm_device_attr.addr the address for SPE buffer overflow interrupt
> +	    is a pointer to an int
> +Returns: -EBUSY: The SPE overflow interrupt is already set
> +         -ENXIO: The overflow interrupt not set when attempting to get it
> +         -ENODEV: SPEv1 not supported
> +         -EINVAL: Invalid SPE overflow interrupt number supplied or
> +                  trying to set the IRQ number without using an in-kernel
> +                  irqchip.
> +
> +A value describing the SPEv1 (Statistical Profiling Extension v1) overflow
> +interrupt number for this vcpu. This interrupt should be PPI and the interrupt
> +type and number must be same for each vcpu.
> +
> +4.2 ATTRIBUTE: KVM_ARM_VCPU_SPE_V1_INIT
> +Parameters: no additional parameter in kvm_device_attr.addr
> +Returns: -ENODEV: SPEv1 not supported or GIC not initialized
> +         -ENXIO: SPEv1 not properly configured or in-kernel irqchip not
> +                 configured as required prior to calling this attribute
> +         -EBUSY: SPEv1 already initialized
> +
> +Request the initialization of the SPEv1.  If using the SPEv1 with an in-kernel
> +virtual GIC implementation, this must be done after initializing the in-kernel
> +irqchip.
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 333c6491bec7..d00f450dc4cd 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -39,7 +39,7 @@
>  
>  #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
>  
> -#define KVM_VCPU_MAX_FEATURES 7
> +#define KVM_VCPU_MAX_FEATURES 8
>  
>  #define KVM_REQ_SLEEP \
>  	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 820e5751ada7..905a73f30079 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -106,6 +106,7 @@ struct kvm_regs {
>  #define KVM_ARM_VCPU_SVE		4 /* enable SVE for this CPU */
>  #define KVM_ARM_VCPU_PTRAUTH_ADDRESS	5 /* VCPU uses address authentication */
>  #define KVM_ARM_VCPU_PTRAUTH_GENERIC	6 /* VCPU uses generic authentication */
> +#define KVM_ARM_VCPU_SPE_V1		7 /* Support guest SPEv1 */
>  
>  struct kvm_vcpu_init {
>  	__u32 target;
> @@ -326,6 +327,9 @@ struct kvm_vcpu_events {
>  #define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1
>  #define KVM_ARM_VCPU_PVTIME_CTRL	2
>  #define   KVM_ARM_VCPU_PVTIME_IPA	0
> +#define KVM_ARM_VCPU_SPE_V1_CTRL	3
> +#define   KVM_ARM_VCPU_SPE_V1_IRQ	0
> +#define   KVM_ARM_VCPU_SPE_V1_INIT	1
>  
>  /* KVM_IRQ_LINE irq field index values */
>  #define KVM_ARM_IRQ_VCPU2_SHIFT		28
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 5ffbdc39e780..526f3bf09321 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -37,3 +37,4 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic/vgic-debug.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/irqchip.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arch_timer.o
>  kvm-$(CONFIG_KVM_ARM_PMU) += $(KVM)/arm/pmu.o
> +kvm-$(CONFIG_KVM_ARM_SPE) += $(KVM)/arm/spe.o
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 2fff06114a8f..50fea538b8bd 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -874,6 +874,8 @@ int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
>  		break;
>  	case KVM_ARM_VCPU_PVTIME_CTRL:
>  		ret = kvm_arm_pvtime_set_attr(vcpu, attr);
> +	case KVM_ARM_VCPU_SPE_V1_CTRL:
> +		ret = kvm_arm_spe_v1_set_attr(vcpu, attr);
>  		break;
>  	default:
>  		ret = -ENXIO;
> @@ -897,6 +899,8 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
>  		break;
>  	case KVM_ARM_VCPU_PVTIME_CTRL:
>  		ret = kvm_arm_pvtime_get_attr(vcpu, attr);
> +	case KVM_ARM_VCPU_SPE_V1_CTRL:
> +		ret = kvm_arm_spe_v1_get_attr(vcpu, attr);
>  		break;
>  	default:
>  		ret = -ENXIO;
> @@ -920,6 +924,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>  		break;
>  	case KVM_ARM_VCPU_PVTIME_CTRL:
>  		ret = kvm_arm_pvtime_has_attr(vcpu, attr);
> +	case KVM_ARM_VCPU_SPE_V1_CTRL:
> +		ret = kvm_arm_spe_v1_has_attr(vcpu, attr);
>  		break;
>  	default:
>  		ret = -ENXIO;
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index f4a8ae918827..cf17aff1489d 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -80,6 +80,9 @@ int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_ARM_INJECT_SERROR_ESR:
>  		r = cpus_have_const_cap(ARM64_HAS_RAS_EXTN);
>  		break;
> +	case KVM_CAP_ARM_SPE_V1:
> +		r = kvm_arm_support_spe_v1();
> +		break;
>  	case KVM_CAP_SET_GUEST_DEBUG:
>  	case KVM_CAP_VCPU_ATTRIBUTES:
>  		r = 1;
> diff --git a/include/kvm/arm_spe.h b/include/kvm/arm_spe.h
> index 30c40b1bc385..d1f3c564dfd0 100644
> --- a/include/kvm/arm_spe.h
> +++ b/include/kvm/arm_spe.h
> @@ -8,6 +8,7 @@
>  
>  #include <uapi/linux/kvm.h>
>  #include <linux/kvm_host.h>
> +#include <linux/cpufeature.h>
>  
>  struct kvm_spe {
>  	int irq_num;
> @@ -18,8 +19,52 @@ struct kvm_spe {
>  
>  #ifdef CONFIG_KVM_ARM_SPE
>  #define kvm_arm_spe_v1_ready(v)		((v)->arch.spe.ready)
> +#define kvm_arm_spe_irq_initialized(v)		\
> +	((v)->arch.spe.irq_num >= VGIC_NR_SGIS &&	\
> +	(v)->arch.spe.irq_num <= VGIC_MAX_PRIVATE)

This is buggy, as it accepts 32 as a valid interrupt (which obviously
isn't a PPI). Having fixed it, this is a duplicate of irq_is_ppi().

And that's where we can finally confirm that 'irq_num' is a GIC
INTID. Please name it as such.

> +
> +static inline bool kvm_arm_support_spe_v1(void)
> +{
> +	u64 dfr0 = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
> +
> +	return !!cpuid_feature_extract_unsigned_field(dfr0,
> +						      ID_AA64DFR0_PMSVER_SHIFT);
> +}
> +
> +int kvm_arm_spe_v1_set_attr(struct kvm_vcpu *vcpu,
> +			    struct kvm_device_attr *attr);
> +int kvm_arm_spe_v1_get_attr(struct kvm_vcpu *vcpu,
> +			    struct kvm_device_attr *attr);
> +int kvm_arm_spe_v1_has_attr(struct kvm_vcpu *vcpu,
> +			    struct kvm_device_attr *attr);
> +int kvm_arm_spe_v1_enable(struct kvm_vcpu *vcpu);
>  #else
>  #define kvm_arm_spe_v1_ready(v)		(false)
> +#define kvm_arm_support_spe_v1()	(false)
> +#define kvm_arm_spe_irq_initialized(v)	(false)
> +
> +static inline int kvm_arm_spe_v1_set_attr(struct kvm_vcpu *vcpu,
> +					  struct kvm_device_attr *attr)
> +{
> +	return -ENXIO;
> +}
> +
> +static inline int kvm_arm_spe_v1_get_attr(struct kvm_vcpu *vcpu,
> +					  struct kvm_device_attr *attr)
> +{
> +	return -ENXIO;
> +}
> +
> +static inline int kvm_arm_spe_v1_has_attr(struct kvm_vcpu *vcpu,
> +					  struct kvm_device_attr *attr)
> +{
> +	return -ENXIO;
> +}
> +
> +static inline int kvm_arm_spe_v1_enable(struct kvm_vcpu *vcpu)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_KVM_ARM_SPE */
>  
>  #endif /* __ASM_ARM_KVM_SPE_H */
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index f0a16b4adbbd..1a362c230e4a 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1009,6 +1009,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_PPC_GUEST_DEBUG_SSTEP 176
>  #define KVM_CAP_ARM_NISV_TO_USER 177
>  #define KVM_CAP_ARM_INJECT_EXT_DABT 178
> +#define KVM_CAP_ARM_SPE_V1 179
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 12e0280291ce..340d2388ee2c 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -22,6 +22,7 @@
>  #include <trace/events/kvm.h>
>  #include <kvm/arm_pmu.h>
>  #include <kvm/arm_psci.h>
> +#include <kvm/arm_spe.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include "trace.h"
> diff --git a/virt/kvm/arm/spe.c b/virt/kvm/arm/spe.c
> new file mode 100644
> index 000000000000..83ac2cce2cc3
> --- /dev/null
> +++ b/virt/kvm/arm/spe.c
> @@ -0,0 +1,163 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 ARM Ltd.
> + */
> +
> +#include <linux/cpu.h>
> +#include <linux/kvm.h>
> +#include <linux/kvm_host.h>
> +#include <linux/uaccess.h>
> +#include <asm/kvm_emulate.h>
> +#include <kvm/arm_spe.h>
> +#include <kvm/arm_vgic.h>
> +
> +int kvm_arm_spe_v1_enable(struct kvm_vcpu *vcpu)
> +{
> +	if (!vcpu->arch.spe.created)
> +		return 0;

Shouldn't it be an error to enable something that doesn't exist?

> +
> +	/*
> +	 * A valid interrupt configuration for the SPE is either to have a

either?

> +	 * properly configured interrupt number and using an in-kernel irqchip.
> +	 */
> +	if (irqchip_in_kernel(vcpu->kvm)) {
> +		int irq = vcpu->arch.spe.irq_num;
> +
> +		if (!kvm_arm_spe_irq_initialized(vcpu))
> +			return -EINVAL;
> +
> +		if (!irq_is_ppi(irq))
> +			return -EINVAL;
> +	}
> +
> +	vcpu->arch.spe.ready = true;

And SPE is then ready even when we don't have an in-kernel irqchip?

> +
> +	return 0;
> +}
> +
> +static int kvm_arm_spe_v1_init(struct kvm_vcpu *vcpu)
> +{
> +	if (!kvm_arm_support_spe_v1())
> +		return -ENODEV;
> +
> +	if (!test_bit(KVM_ARM_VCPU_SPE_V1, vcpu->arch.features))
> +		return -ENXIO;
> +
> +	if (vcpu->arch.spe.created)
> +		return -EBUSY;
> +
> +	if (irqchip_in_kernel(vcpu->kvm)) {
> +		int ret;
> +
> +		/*
> +		 * If using the SPE with an in-kernel virtual GIC
> +		 * implementation, we require the GIC to be already
> +		 * initialized when initializing the SPE.
> +		 */
> +		if (!vgic_initialized(vcpu->kvm))
> +			return -ENODEV;
> +
> +		ret = kvm_vgic_set_owner(vcpu, vcpu->arch.spe.irq_num,
> +					 &vcpu->arch.spe);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	vcpu->arch.spe.created = true;

Same problem.

> +	return 0;
> +}
> +
> +/*
> + * For one VM the interrupt type must be same for each vcpu.
> + * As a PPI, the interrupt number is the same for all vcpus,
> + * while as an SPI it must be a separate number per vcpu.

Why do you want to support SPIs at all? And it isn't what
kvm_arm_spe_irq_initialized claims to be doing.

> + */
> +static bool spe_irq_is_valid(struct kvm *kvm, int irq)
> +{
> +	int i;
> +	struct kvm_vcpu *vcpu;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (!kvm_arm_spe_irq_initialized(vcpu))
> +			continue;
> +
> +		if (vcpu->arch.spe.irq_num != irq)
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
> +int kvm_arm_spe_v1_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> +{
> +	switch (attr->attr) {
> +	case KVM_ARM_VCPU_SPE_V1_IRQ: {
> +		int __user *uaddr = (int __user *)(long)attr->addr;
> +		int irq;
> +
> +		if (!irqchip_in_kernel(vcpu->kvm))
> +			return -EINVAL;

Here, you forbid setting the IRQ for a VM that doesn't have an
in-kernel irqchip. And yet below, you're happy to initialise it.

> +
> +		if (!test_bit(KVM_ARM_VCPU_SPE_V1, vcpu->arch.features))
> +			return -ENODEV;
> +
> +		if (get_user(irq, uaddr))
> +			return -EFAULT;
> +
> +		/* The SPE overflow interrupt can be a PPI only */
> +		if (!(irq_is_ppi(irq)))
> +			return -EINVAL;

Ah, so you do know about irq_is_ppi()...

> +
> +		if (!spe_irq_is_valid(vcpu->kvm, irq))

But why don't you fold the interrupt validity checks in this helper?

> +			return -EINVAL;
> +
> +		if (kvm_arm_spe_irq_initialized(vcpu))
> +			return -EBUSY;
> +
> +		kvm_debug("Set kvm ARM SPE irq: %d\n", irq);
> +		vcpu->arch.spe.irq_num = irq;
> +		return 0;
> +	}
> +	case KVM_ARM_VCPU_SPE_V1_INIT:
> +		return kvm_arm_spe_v1_init(vcpu);
> +	}
> +
> +	return -ENXIO;
> +}
> +
> +int kvm_arm_spe_v1_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> +{
> +	switch (attr->attr) {
> +	case KVM_ARM_VCPU_SPE_V1_IRQ: {
> +		int __user *uaddr = (int __user *)(long)attr->addr;
> +		int irq;
> +
> +		if (!irqchip_in_kernel(vcpu->kvm))
> +			return -EINVAL;
> +
> +		if (!test_bit(KVM_ARM_VCPU_SPE_V1, vcpu->arch.features))
> +			return -ENODEV;
> +
> +		if (!kvm_arm_spe_irq_initialized(vcpu))
> +			return -ENXIO;
> +
> +		irq = vcpu->arch.spe.irq_num;
> +		return put_user(irq, uaddr);
> +	}
> +	}
> +
> +	return -ENXIO;
> +}
> +
> +int kvm_arm_spe_v1_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> +{
> +	switch (attr->attr) {
> +	case KVM_ARM_VCPU_SPE_V1_IRQ:
> +	case KVM_ARM_VCPU_SPE_V1_INIT:
> +		if (kvm_arm_support_spe_v1() &&
> +		    test_bit(KVM_ARM_VCPU_SPE_V1, vcpu->arch.features))
> +			return 0;

It is interesting that all the user interface is designed with the
feature being optional in mind, and yet you've removed all the
necessary handling code.

	M.

-- 
Jazz is not dead, it just smells funny.

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