Re: [PATCH v19 014/130] KVM: Add KVM vcpu ioctl to pre-populate guest memory

[Yin Fengwei]

On 2/26/24 16:25, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> Add new ioctl KVM_MEMORY_MAPPING in the kvm common code. It iterates on the
> memory range and call arch specific function.  Add stub function as weak
> symbol.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
> v19:
> - newly added
> ---
>  include/linux/kvm_host.h |  4 +++
>  include/uapi/linux/kvm.h | 10 ++++++
>  virt/kvm/kvm_main.c      | 67 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 81 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0520cd8d03cc..eeaf4e73317c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2389,4 +2389,8 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
>  }
>  #endif /* CONFIG_KVM_PRIVATE_MEM */
>  
> +void kvm_arch_vcpu_pre_memory_mapping(struct kvm_vcpu *vcpu);
> +int kvm_arch_vcpu_memory_mapping(struct kvm_vcpu *vcpu,
> +				 struct kvm_memory_mapping *mapping);
> +
>  #endif
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index c3308536482b..5e2b28934aa9 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1155,6 +1155,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_MEMORY_ATTRIBUTES 233
>  #define KVM_CAP_GUEST_MEMFD 234
>  #define KVM_CAP_VM_TYPES 235
> +#define KVM_CAP_MEMORY_MAPPING 236
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -2227,4 +2228,13 @@ struct kvm_create_guest_memfd {
>  	__u64 reserved[6];
>  };
>  
> +#define KVM_MEMORY_MAPPING	_IOWR(KVMIO, 0xd5, struct kvm_memory_mapping)
> +
> +struct kvm_memory_mapping {
> +	__u64 base_gfn;
> +	__u64 nr_pages;
> +	__u64 flags;
> +	__u64 source;
> +};
> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 0349e1f241d1..2f0a8e28795e 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4409,6 +4409,62 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
>  	return fd;
>  }
>  
> +__weak void kvm_arch_vcpu_pre_memory_mapping(struct kvm_vcpu *vcpu)
> +{
> +}
> +
> +__weak int kvm_arch_vcpu_memory_mapping(struct kvm_vcpu *vcpu,
> +					struct kvm_memory_mapping *mapping)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int kvm_vcpu_memory_mapping(struct kvm_vcpu *vcpu,
> +				   struct kvm_memory_mapping *mapping)
> +{
> +	bool added = false;
> +	int idx, r = 0;
> +
> +	/* flags isn't used yet. */
> +	if (mapping->flags)
> +		return -EINVAL;
> +
> +	/* Sanity check */
> +	if (!IS_ALIGNED(mapping->source, PAGE_SIZE) ||
> +	    !mapping->nr_pages ||
> +	    mapping->nr_pages & GENMASK_ULL(63, 63 - PAGE_SHIFT) ||
> +	    mapping->base_gfn + mapping->nr_pages <= mapping->base_gfn)
I suppose !mapping->nr_pages can be deleted as this line can cover it.
> +		return -EINVAL;
> +
> +	vcpu_load(vcpu);
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
> +	kvm_arch_vcpu_pre_memory_mapping(vcpu);
> +
> +	while (mapping->nr_pages) {
> +		if (signal_pending(current)) {
> +			r = -ERESTARTSYS;
> +			break;
> +		}
> +
> +		if (need_resched())
> +			cond_resched();
> +
> +		r = kvm_arch_vcpu_memory_mapping(vcpu, mapping);
> +		if (r)
> +			break;
> +
> +		added = true;
> +	}
> +
> +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
> +	vcpu_put(vcpu);
> +
> +	if (added && mapping->nr_pages > 0)
> +		r = -EAGAIN;
> +
> +	return r;
> +}
> +
>  static long kvm_vcpu_ioctl(struct file *filp,
>  			   unsigned int ioctl, unsigned long arg)
>  {
> @@ -4610,6 +4666,17 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
>  		break;
>  	}
> +	case KVM_MEMORY_MAPPING: {
> +		struct kvm_memory_mapping mapping;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&mapping, argp, sizeof(mapping)))
> +			break;
> +		r = kvm_vcpu_memory_mapping(vcpu, &mapping);
return value r should be checked before copy_to_user


Regards
Yin, Fengwei

> +		if (copy_to_user(argp, &mapping, sizeof(mapping)))
> +			r = -EFAULT;
> +		break;
> +	}
>  	default:
>  		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
>  	}