linux-kernel - Re: [PATCH 2/7] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate guest memory

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Message-ID: <20240417193625.GJ3039520@ls.amr.corp.intel.com>
Date: Wed, 17 Apr 2024 12:36:25 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	isaku.yamahata@...el.com, xiaoyao.li@...el.com,
	binbin.wu@...ux.intel.com, seanjc@...gle.com,
	rick.p.edgecombe@...el.com, isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH 2/7] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate
 guest memory

On Wed, Apr 17, 2024 at 11:34:45AM -0400,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Add a new ioctl KVM_MAP_MEMORY in the KVM common code. It iterates on the
> memory range and calls the arch-specific function.  Add stub arch function
> as a weak symbol.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Message-ID: <819322b8f25971f2b9933bfa4506e618508ad782.1712785629.git.isaku.yamahata@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  include/linux/kvm_host.h |  5 ++++
>  include/uapi/linux/kvm.h | 10 +++++++
>  virt/kvm/Kconfig         |  3 ++
>  virt/kvm/kvm_main.c      | 61 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 79 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8dea11701ab2..2b0f0240a64c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2478,4 +2478,9 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t gfn, void __user *src, long npages
>  void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
>  #endif
>  
> +#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
> +int kvm_arch_vcpu_map_memory(struct kvm_vcpu *vcpu,
> +			     struct kvm_map_memory *mapping);
> +#endif
> +
>  #endif
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 2190adbe3002..4d233f44c613 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -917,6 +917,7 @@ struct kvm_enable_cap {
>  #define KVM_CAP_MEMORY_ATTRIBUTES 233
>  #define KVM_CAP_GUEST_MEMFD 234
>  #define KVM_CAP_VM_TYPES 235
> +#define KVM_CAP_MAP_MEMORY 236
>  
>  struct kvm_irq_routing_irqchip {
>  	__u32 irqchip;
> @@ -1548,4 +1549,13 @@ struct kvm_create_guest_memfd {
>  	__u64 reserved[6];
>  };
>  
> +#define KVM_MAP_MEMORY	_IOWR(KVMIO, 0xd5, struct kvm_map_memory)
> +
> +struct kvm_map_memory {
> +	__u64 base_address;
> +	__u64 size;
> +	__u64 flags;
> +	__u64 padding[5];
> +};
> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 754c6c923427..1b94126622e8 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -67,6 +67,9 @@ config HAVE_KVM_INVALID_WAKEUPS
>  config KVM_GENERIC_DIRTYLOG_READ_PROTECT
>         bool
>  
> +config KVM_GENERIC_MAP_MEMORY
> +       bool
> +
>  config KVM_COMPAT
>         def_bool y
>         depends on KVM && COMPAT && !(S390 || ARM64 || RISCV)
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 38b498669ef9..350ead98e9a6 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4379,6 +4379,47 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
>  	return fd;
>  }
>  
> +#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
> +static int kvm_vcpu_map_memory(struct kvm_vcpu *vcpu,
> +			       struct kvm_map_memory *mapping)
> +{
> +	int idx, r;
> +	u64 full_size;
> +
> +	if (mapping->flags)
> +		return -EINVAL;
> +
> +	if (!PAGE_ALIGNED(mapping->base_address) ||
> +	    !PAGE_ALIGNED(mapping->size) ||
> +	    mapping->base_address + mapping->size <= mapping->base_address)
> +		return -EINVAL;
> +
> +	vcpu_load(vcpu);
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
> +
> +	r = 0;
> +	full_size = mapping->size;
> +	while (mapping->size) {
> +		if (signal_pending(current)) {
> +			r = -EINTR;
> +			break;
> +		}
> +
> +		r = kvm_arch_vcpu_map_memory(vcpu, mapping);
> +		if (r)
> +			break;
> +
> +		cond_resched();
> +	}
> +
> +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
> +	vcpu_put(vcpu);
> +
> +	/* Return success if at least one page was mapped successfully.  */
> +	return full_size == mapping->size ? r : 0;
> +}
> +#endif
> +
>  static long kvm_vcpu_ioctl(struct file *filp,
>  			   unsigned int ioctl, unsigned long arg)
>  {
> @@ -4580,6 +4621,20 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
>  		break;
>  	}
> +#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
> +	case KVM_MAP_MEMORY: {
> +		struct kvm_map_memory mapping;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&mapping, argp, sizeof(mapping)))
> +			break;
> +		r = kvm_vcpu_map_memory(vcpu, &mapping);
> +		/* Pass back leftover range. */
> +		if (copy_to_user(argp, &mapping, sizeof(mapping)))
> +			r = -EFAULT;
> +		break;
> +	}
> +#endif
>  	default:
>  		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
>  	}
> @@ -4863,6 +4918,12 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  #ifdef CONFIG_KVM_PRIVATE_MEM
>  	case KVM_CAP_GUEST_MEMFD:
>  		return !kvm || kvm_arch_has_private_mem(kvm);
> +#endif
> +#ifdef CONFIG_KVM_GENERIC_MAP_MEMORY
> +	case KVM_CAP_MAP_MEMORY:
> +		if (!kvm)
> +			return 1;
> +		/* Leave per-VM implementation to kvm_vm_ioctl_check_extension().  */

nitpick:
                fallthough;

>  #endif
>  	default:
>  		break;
> -- 
> 2.43.0
> 
> 
> 

-- 
Isaku Yamahata <isaku.yamahata@...el.com>