linux-kernel - Re: [PATCH v9 13/18] KVM: s390: pv: cleanup leftover protected VMs if needed

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Date:   Thu, 31 Mar 2022 16:02:55 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, thuth@...hat.com, pasic@...ux.ibm.com,
        david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, scgl@...ux.ibm.com,
        mimu@...ux.ibm.com, nrb@...ux.ibm.com
Subject: Re: [PATCH v9 13/18] KVM: s390: pv: cleanup leftover protected VMs if
 needed

On 3/30/22 14:26, Claudio Imbrenda wrote:
> In upcoming patches it will be possible to start tearing down a
> protected VM, and finish the teardown concurrently in a different
> thread.
> 
> Protected VMs that are pending for tear down ("leftover") need to be
> cleaned properly when the userspace process (e.g. qemu) terminates.
> 
> This patch makes sure that all "leftover" protected VMs are always
> properly torn down.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>   arch/s390/include/asm/kvm_host.h |  2 +
>   arch/s390/kvm/kvm-s390.c         |  1 +
>   arch/s390/kvm/pv.c               | 69 ++++++++++++++++++++++++++++++++
>   3 files changed, 72 insertions(+)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 1bccb8561ba9..50e3516cbc03 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -922,6 +922,8 @@ struct kvm_s390_pv {
>   	u64 guest_len;
>   	unsigned long stor_base;
>   	void *stor_var;
> +	void *async_deinit;
> +	struct list_head need_cleanup;
>   	struct mmu_notifier mmu_notifier;
>   };
>   
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 446f89db93a1..3637f556ff33 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2788,6 +2788,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	kvm_s390_vsie_init(kvm);
>   	if (use_gisa)
>   		kvm_s390_gisa_init(kvm);
> +	INIT_LIST_HEAD(&kvm->arch.pv.need_cleanup);

kvm->arch.pv.sync_deinit = NULL;

>   	KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>   
>   	return 0;
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index be3b467f8feb..56412617dd01 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -17,6 +17,19 @@
>   #include <linux/mmu_notifier.h>
>   #include "kvm-s390.h"
>   
> +/**
> + * @struct deferred_priv
> + * Represents a "leftover" protected VM that does not correspond to any
> + * active KVM VM.

Maybe something like:
...that is still registered with the Ultravisor but isn't registered 
with KVM anymore.

> + */
> +struct deferred_priv {
> +	struct list_head list;
> +	unsigned long old_table;
> +	u64 handle;
> +	void *stor_var;
> +	unsigned long stor_base;
> +};
> +
>   static void kvm_s390_clear_pv_state(struct kvm *kvm)
>   {
>   	kvm->arch.pv.handle = 0;
> @@ -163,6 +176,60 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
>   	return -ENOMEM;
>   }
>   
> +/**
> + * kvm_s390_pv_cleanup_deferred - Clean up one leftover protected VM.
> + * @kvm the KVM that was associated with this leftover protected VM
> + * @deferred details about the leftover protected VM that needs a clean up
> + * Return: 0 in case of success, otherwise 1
> + */
> +static int kvm_s390_pv_cleanup_deferred(struct kvm *kvm, struct deferred_priv *deferred)
> +{
> +	u16 rc, rrc;
> +	int cc;
> +
> +	cc = uv_cmd_nodata(deferred->handle, UVC_CMD_DESTROY_SEC_CONF, &rc, &rrc);
> +	KVM_UV_EVENT(kvm, 3, "PROTVIRT DESTROY VM: rc %x rrc %x", rc, rrc);
> +	WARN_ONCE(cc, "protvirt destroy vm failed rc %x rrc %x", rc, rrc);
> +	if (cc)
> +		return cc;
> +	/*
> +	 * Intentionally leak unusable memory. If the UVC fails, the memory
> +	 * used for the VM and its metadata is permanently unusable.
> +	 * This can only happen in case of a serious KVM or hardware bug; it
> +	 * is not expected to happen in normal operation.
> +	 */
> +	free_pages(deferred->stor_base, get_order(uv_info.guest_base_stor_len));
> +	free_pages(deferred->old_table, CRST_ALLOC_ORDER);
> +	vfree(deferred->stor_var);
> +	return 0;
> +}
> +
> +/**
> + * kvm_s390_pv_cleanup_leftovers - Clean up all leftover protected VMs.
> + * @kvm the KVM whose leftover protected VMs are to be cleaned up
> + * Return: 0 in case of success, otherwise 1
> + */
> +static int kvm_s390_pv_cleanup_leftovers(struct kvm *kvm)
> +{
> +	struct deferred_priv *deferred;
> +	int cc = 0;
> +
> +	if (kvm->arch.pv.async_deinit)
> +		list_add(kvm->arch.pv.async_deinit, &kvm->arch.pv.need_cleanup);
> +
> +	while (!list_empty(&kvm->arch.pv.need_cleanup)) {
> +		deferred = list_first_entry(&kvm->arch.pv.need_cleanup, typeof(*deferred), list);
> +		if (kvm_s390_pv_cleanup_deferred(kvm, deferred))
> +			cc = 1;
> +		else
> +			atomic_dec(&kvm->mm->context.protected_count);
> +		list_del(&deferred->list);
> +		kfree(deferred);
> +	}
> +	kvm->arch.pv.async_deinit = NULL;
> +	return cc;
> +}
> +
>   /* this should not fail, but if it does, we must not free the donated memory */
>   int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>   {
> @@ -190,6 +257,8 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>   	KVM_UV_EVENT(kvm, 3, "PROTVIRT DESTROY VM: rc %x rrc %x", *rc, *rrc);
>   	WARN_ONCE(cc, "protvirt destroy vm failed rc %x rrc %x", *rc, *rrc);
>   
> +	cc |= kvm_s390_pv_cleanup_leftovers(kvm);
> +
>   	return cc ? -EIO : 0;
>   }
>