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SubjectRe: [PATCH v4 07/10] KVM: arm64: Provide VCPU attributes for stolen time
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On 30/08/2019 09:42, Steven Price wrote:
> Allow user space to inform the KVM host where in the physical memory
> map the paravirtualized time structures should be located.
>
> User space can set an attribute on the VCPU providing the IPA base
> address of the stolen time structure for that VCPU. This must be
> repeated for every VCPU in the VM.
>
> The address is given in terms of the physical address visible to
> the guest and must be 64 byte aligned. The guest will discover the
> address via a hypercall.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> arch/arm64/include/asm/kvm_host.h | 7 +++++
> arch/arm64/include/uapi/asm/kvm.h | 2 ++
> arch/arm64/kvm/guest.c | 9 ++++++
> include/uapi/linux/kvm.h | 2 ++
> virt/kvm/arm/pvtime.c | 47 +++++++++++++++++++++++++++++++
> 5 files changed, 67 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 1697e63f6dd8..6af16b29a41f 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -489,6 +489,13 @@ long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu);
> long kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu);
> int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init);
>
> +int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr);
> +int kvm_arm_pvtime_get_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr);
> +int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr);
> +
> static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
> {
> vcpu_arch->steal.base = GPA_INVALID;
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 9a507716ae2f..bde9f165ad3a 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -323,6 +323,8 @@ struct kvm_vcpu_events {
> #define KVM_ARM_VCPU_TIMER_CTRL 1
> #define KVM_ARM_VCPU_TIMER_IRQ_VTIMER 0
> #define KVM_ARM_VCPU_TIMER_IRQ_PTIMER 1
> +#define KVM_ARM_VCPU_PVTIME_CTRL 2
> +#define KVM_ARM_VCPU_PVTIME_SET_IPA 0
>
> /* KVM_IRQ_LINE irq field index values */
> #define KVM_ARM_IRQ_TYPE_SHIFT 24
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index dfd626447482..d3ac9d2fd405 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -858,6 +858,9 @@ int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
> case KVM_ARM_VCPU_TIMER_CTRL:
> ret = kvm_arm_timer_set_attr(vcpu, attr);
> break;
> + case KVM_ARM_VCPU_PVTIME_CTRL:
> + ret = kvm_arm_pvtime_set_attr(vcpu, attr);
> + break;
> default:
> ret = -ENXIO;
> break;
> @@ -878,6 +881,9 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
> case KVM_ARM_VCPU_TIMER_CTRL:
> ret = kvm_arm_timer_get_attr(vcpu, attr);
> break;
> + case KVM_ARM_VCPU_PVTIME_CTRL:
> + ret = kvm_arm_pvtime_get_attr(vcpu, attr);
> + break;
> default:
> ret = -ENXIO;
> break;
> @@ -898,6 +904,9 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
> case KVM_ARM_VCPU_TIMER_CTRL:
> ret = kvm_arm_timer_has_attr(vcpu, attr);
> break;
> + case KVM_ARM_VCPU_PVTIME_CTRL:
> + ret = kvm_arm_pvtime_has_attr(vcpu, attr);
> + break;
> default:
> ret = -ENXIO;
> break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 5e3f12d5359e..265156a984f2 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1222,6 +1222,8 @@ enum kvm_device_type {
> #define KVM_DEV_TYPE_ARM_VGIC_ITS KVM_DEV_TYPE_ARM_VGIC_ITS
> KVM_DEV_TYPE_XIVE,
> #define KVM_DEV_TYPE_XIVE KVM_DEV_TYPE_XIVE
> + KVM_DEV_TYPE_ARM_PV_TIME,
> +#define KVM_DEV_TYPE_ARM_PV_TIME KVM_DEV_TYPE_ARM_PV_TIME
> KVM_DEV_TYPE_MAX,
> };
>
> diff --git a/virt/kvm/arm/pvtime.c b/virt/kvm/arm/pvtime.c
> index d9d0dbc6994b..7b1834b98a68 100644
> --- a/virt/kvm/arm/pvtime.c
> +++ b/virt/kvm/arm/pvtime.c
> @@ -2,7 +2,9 @@
> // Copyright (C) 2019 Arm Ltd.
>
> #include <linux/arm-smccc.h>
> +#include <linux/kvm_host.h>
>
> +#include <asm/kvm_mmu.h>
> #include <asm/pvclock-abi.h>
>
> #include <kvm/arm_hypercalls.h>
> @@ -75,3 +77,48 @@ long kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)
>
> return vcpu->arch.steal.base;
> }
> +
> +int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr)
> +{
> + u64 __user *user = (u64 __user *)attr->addr;
> + u64 ipa;
> +
> + if (attr->attr != KVM_ARM_VCPU_PVTIME_SET_IPA)
> + return -ENXIO;
> +
> + if (get_user(ipa, user))
> + return -EFAULT;
> + if (ipa & 63)

nit: Please express this as !IS_ALIGNED(ipa, 64) instead.

> + return -EINVAL;
> + if (vcpu->arch.steal.base != GPA_INVALID)
> + return -EEXIST;
> + vcpu->arch.steal.base = ipa;

I'm still worried that you end-up not knowing whether the IPA is valid
or not at this stage, nor that we check about overlapping vcpus. How do
we validate that?

I also share Christoffer's concern that the memslot parsing may be
expensive on a system with multiple memslots. But maybe that can be
solved by adding some caching capabilities to your kvm_put_guest(),
should this become a problem.

> + return 0;
> +}
> +
> +int kvm_arm_pvtime_get_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr)
> +{
> + u64 __user *user = (u64 __user *)attr->addr;
> + u64 ipa;
> +
> + if (attr->attr != KVM_ARM_VCPU_PVTIME_SET_IPA)

It is a bit odd that this is using "SET_IPA" as a way to GET it.

> + return -ENXIO;
> +
> + ipa = vcpu->arch.steal.base;
> +
> + if (put_user(ipa, user))
> + return -EFAULT;
> + return 0;
> +}
> +
> +int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu,
> + struct kvm_device_attr *attr)
> +{
> + switch (attr->attr) {
> + case KVM_ARM_VCPU_PVTIME_SET_IPA:
> + return 0;
> + }
> + return -ENXIO;
> +}
>

Thanks,

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

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