Re: [PATCH 2/6] KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory

[Isaku Yamahata <isaku.yamahata@intel.com>]

On Fri, Apr 19, 2024 at 04:59:23AM -0400,
Paolo Bonzini <pbonzini@redhat.com> wrote:

> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> Add a new ioctl KVM_PRE_FAULT_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@google.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Message-ID: <819322b8f25971f2b9933bfa4506e618508ad782.1712785629.git.isaku.yamahata@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  include/linux/kvm_host.h |  5 ++++
>  include/uapi/linux/kvm.h | 10 +++++++
>  virt/kvm/Kconfig         |  3 ++
>  virt/kvm/kvm_main.c      | 63 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 81 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8dea11701ab2..9e9943e5e37c 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_PRE_FAULT_MEMORY
> +long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
> +				    struct kvm_pre_fault_memory *range);
> +#endif
> +
>  #endif
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 2190adbe3002..917d2964947d 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_PRE_FAULT_MEMORY 236
>  
>  struct kvm_irq_routing_irqchip {
>  	__u32 irqchip;
> @@ -1548,4 +1549,13 @@ struct kvm_create_guest_memfd {
>  	__u64 reserved[6];
>  };
>  
> +#define KVM_PRE_FAULT_MEMORY	_IOWR(KVMIO, 0xd5, struct kvm_pre_fault_memory)
> +
> +struct kvm_pre_fault_memory {
> +	__u64 gpa;
> +	__u64 size;
> +	__u64 flags;
> +	__u64 padding[5];
> +};
> +
>  #endif /* __LINUX_KVM_H */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 754c6c923427..b14e14cdbfb9 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_PRE_FAULT_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..51d8dbe7e93b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4379,6 +4379,55 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
>  	return fd;
>  }
>  
> +#ifdef CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY
> +static int kvm_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
> +				     struct kvm_pre_fault_memory *range)
> +{
> +	int idx;
> +	long r;
> +	u64 full_size;
> +
> +	if (range->flags)
> +		return -EINVAL;

To keep future extensively, check the padding are zero.
Or will we be rely on flags?

        if (!memchr_inv(range->padding, 0, sizeof(range->padding)))
                return -EINVAL;
-- 
Isaku Yamahata <isaku.yamahata@intel.com>