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

Yin Fengwei
2024-03-07T07:01:17Z

On 2/26/24 16:25, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
>
> 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@intel.com>
> ---
> 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);
> }