Message-ID: <0cd04469-d840-0cc7-8faf-8f07aa2dd876@linux.ibm.com>
Date:   Tue, 4 Oct 2022 15:43:29 +0200
From:   Steffen Eiden <seiden@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, frankja@...ux.ibm.com, thuth@...hat.com,
        david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, scgl@...ux.ibm.com, nrb@...ux.ibm.com
Subject: Re: [PATCH v14 1/6] KVM: s390: pv: asynchronous destroy for reboot

Hi Claudio,

LGTM, but I have some nits.

On 9/30/22 16:01, Claudio Imbrenda wrote:
> Until now, destroying a protected guest was an entirely synchronous
> operation that could potentially take a very long time, depending on
> the size of the guest, due to the time needed to clean up the address
> space from protected pages.
> 
> This patch implements an asynchronous destroy mechanism, that allows a
> protected guest to reboot significantly faster than previously.
> 
> This is achieved by clearing the pages of the old guest in background.
> In case of reboot, the new guest will be able to run in the same
> address space almost immediately.
> 
> The old protected guest is then only destroyed when all of its memory
> has been destroyed or otherwise made non protected.
> 
> Two new PV commands are added for the KVM_S390_PV_COMMAND ioctl:
> 
> KVM_PV_ASYNC_CLEANUP_PREPARE: set aside the current protected VM for
> later asynchronous teardown. The current KVM VM will then continue
> immediately as non-protected. If a protected VM had already been
> set aside for asynchronous teardown, but without starting the teardown
> process, this call will fail. There can be at most one VM set aside at
> any time. Once it is set aside, the protected VM only exists in the
> context of the Ultravisor, it is not associated with the KVM VM
> anymore. Its protected CPUs have already been destroyed, but not its
> memory. This command can be issued again immediately after starting
> KVM_PV_ASYNC_CLEANUP_PERFORM, without having to wait for completion.
> 
> KVM_PV_ASYNC_CLEANUP_PERFORM: tears down the protected VM previously
> set aside using KVM_PV_ASYNC_CLEANUP_PREPARE. Ideally the
> KVM_PV_ASYNC_CLEANUP_PERFORM PV command should be issued by userspace
> from a separate thread. If a fatal signal is received (or if the
> process terminates naturally), the command will terminate immediately
> without completing. All protected VMs whose teardown was interrupted
> will be put in the need_cleanup list. The rest of the normal KVM
> teardown process will take care of properly cleaning up all remaining
> protected VMs, including the ones on the need_cleanup list.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Reviewed-by: Nico Boehr <nrb@...ux.ibm.com>
With nits fixed/discussed:
Reviewed-by: Steffen Eiden <seiden@...ux.ibm.com>

> ---
>   arch/s390/include/asm/kvm_host.h |   2 +
>   arch/s390/kvm/kvm-s390.c         |  49 +++++-
>   arch/s390/kvm/kvm-s390.h         |   3 +
>   arch/s390/kvm/pv.c               | 290 +++++++++++++++++++++++++++++--
>   include/uapi/linux/kvm.h         |   2 +
>   5 files changed, 328 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index b1e98a9ed152..470521b8df76 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -942,6 +942,8 @@ struct kvm_s390_pv {
>   	unsigned long stor_base;
>   	void *stor_var;
>   	bool dumping;
> +	void *set_aside;
> +	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 b7ef0b71014d..d0027964a6f5 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -209,6 +209,8 @@ unsigned int diag9c_forwarding_hz;
>   module_param(diag9c_forwarding_hz, uint, 0644);
>   MODULE_PARM_DESC(diag9c_forwarding_hz, "Maximum diag9c forwarding per second, 0 to turn off");
>

IMO it would be better to initialize this variable explicitly here.
You do this later in patch [6/6].
Whats the reason to do this not at this point.


> +static int async_destroy;
> +
>   /*
>    * For now we handle at most 16 double words as this is what the s390 base
>    * kernel handles and stores in the prefix page. If we ever need to go beyond
> @@ -2504,9 +2506,13 @@ static int kvm_s390_pv_dmp(struct kvm *kvm, struct kvm_pv_cmd *cmd,
>   
>   static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>   {
> +	const bool needslock = (cmd->cmd != KVM_PV_ASYNC_CLEANUP_PERFORM);
`need_lock` ? or just `lock` ?
> +	void __user *argp = (void __user *)cmd->data;
>   	int r = 0;
>   	u16 dummy;
> -	void __user *argp = (void __user *)cmd->data;
> +
> +	if (needslock)
> +		mutex_lock(&kvm->lock);
>   
>   	switch (cmd->cmd) {
>   	case KVM_PV_ENABLE: {
> @@ -2540,6 +2546,31 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>   		set_bit(IRQ_PEND_EXT_SERVICE, &kvm->arch.float_int.masked_irqs);
>   		break;
>   	}
> +	case KVM_PV_ASYNC_CLEANUP_PREPARE:
> +		r = -EINVAL;
> +		if (!kvm_s390_pv_is_protected(kvm) || !async_destroy)
> +			break;
> +
> +		r = kvm_s390_cpus_from_pv(kvm, &cmd->rc, &cmd->rrc);
> +		/*
> +		 * If a CPU could not be destroyed, destroy VM will also fail.
> +		 * There is no point in trying to destroy it. Instead return
> +		 * the rc and rrc from the first CPU that failed destroying.
> +		 */
> +		if (r)
> +			break;
> +		r = kvm_s390_pv_set_aside(kvm, &cmd->rc, &cmd->rrc);
> +
> +		/* no need to block service interrupts any more */
> +		clear_bit(IRQ_PEND_EXT_SERVICE, &kvm->arch.float_int.masked_irqs);
> +		break;
> +	case KVM_PV_ASYNC_CLEANUP_PERFORM:
> +		r = -EINVAL;
> +		if (!async_destroy)
> +			break;
> +		/* kvm->lock must not be held; this is asserted inside the function. */
> +		r = kvm_s390_pv_deinit_aside_vm(kvm, &cmd->rc, &cmd->rrc);
> +		break;
>   	case KVM_PV_DISABLE: {
>   		r = -EINVAL;
>   		if (!kvm_s390_pv_is_protected(kvm))
> @@ -2553,7 +2584,7 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>   		 */
>   		if (r)
>   			break;
> -		r = kvm_s390_pv_deinit_vm(kvm, &cmd->rc, &cmd->rrc);
> +		r = kvm_s390_pv_deinit_cleanup_all(kvm, &cmd->rc, &cmd->rrc);
>   
>   		/* no need to block service interrupts any more */
>   		clear_bit(IRQ_PEND_EXT_SERVICE, &kvm->arch.float_int.masked_irqs);
> @@ -2703,6 +2734,9 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>   	default:
>   		r = -ENOTTY;
>   	}
> +	if (needslock)
> +		mutex_unlock(&kvm->lock);
> +
>   	return r;
>   }
>   
> @@ -2907,9 +2941,8 @@ long kvm_arch_vm_ioctl(struct file *filp,
>   			r = -EINVAL;
>   			break;
>   		}
> -		mutex_lock(&kvm->lock);
> +		/* must be called without kvm->lock */
>   		r = kvm_s390_handle_pv(kvm, &args);
> -		mutex_unlock(&kvm->lock);
>   		if (copy_to_user(argp, &args, sizeof(args))) {
>   			r = -EFAULT;
>   			break;
> @@ -3228,6 +3261,8 @@ 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.set_aside = NULL;
>   	KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>   
>   	return 0;
> @@ -3272,11 +3307,9 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>   	/*
>   	 * We are already at the end of life and kvm->lock is not taken.
>   	 * This is ok as the file descriptor is closed by now and nobody
> -	 * can mess with the pv state. To avoid lockdep_assert_held from
> -	 * complaining we do not use kvm_s390_pv_is_protected.
> +	 * can mess with the pv state.
>   	 */
> -	if (kvm_s390_pv_get_handle(kvm))
> -		kvm_s390_pv_deinit_vm(kvm, &rc, &rrc);
> +	kvm_s390_pv_deinit_cleanup_all(kvm, &rc, &rrc);
>   	/*
>   	 * Remove the mmu notifier only when the whole KVM VM is torn down,
>   	 * and only if one was registered to begin with. If the VM is
> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
> index f6fd668f887e..e70b895f640e 100644
> --- a/arch/s390/kvm/kvm-s390.h
> +++ b/arch/s390/kvm/kvm-s390.h
> @@ -243,6 +243,9 @@ static inline u32 kvm_s390_get_gisa_desc(struct kvm *kvm)
>   /* implemented in pv.c */
>   int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc);
>   int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc);
> +int kvm_s390_pv_set_aside(struct kvm *kvm, u16 *rc, u16 *rrc);
> +int kvm_s390_pv_deinit_aside_vm(struct kvm *kvm, u16 *rc, u16 *rrc);
> +int kvm_s390_pv_deinit_cleanup_all(struct kvm *kvm, u16 *rc, u16 *rrc);
>   int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc);
>   int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc);
>   int kvm_s390_pv_set_sec_parms(struct kvm *kvm, void *hdr, u64 length, u16 *rc,
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 7cb7799a0acb..335eeec6e3da 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -18,6 +18,29 @@
>   #include <linux/mmu_notifier.h>
>   #include "kvm-s390.h"
>   
> +/**
> + * struct pv_vm_to_be_destroyed - Represents a protected VM that needs to
> + * be destroyed
> + *
> + * @list: list head for the list of leftover VMs
> + * @old_gmap_table: the gmap table of the leftover protected VM
> + * @handle: the handle of the leftover protected VM
> + * @stor_var: pointer to the variable storage of the leftover protected VM
> + * @stor_base: address of the base storage of the leftover protected VM
> + *
> + * Represents a protected VM that is still registered with the Ultravisor,
> + * but which does not correspond any longer to an active KVM VM. It should
> + * be destroyed at some point later, either asynchronously or when the
> + * process terminates.
> + */
> +struct pv_vm_to_be_destroyed {
> +	struct list_head list;
> +	unsigned long old_gmap_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;
> @@ -159,23 +182,149 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
>   	return -ENOMEM;
>   }
>   
> -/* 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)
> +/**
> + * kvm_s390_pv_dispose_one_leftover - Clean up one leftover protected VM.
> + * @kvm: the KVM that was associated with this leftover protected VM
> + * @leftover: details about the leftover protected VM that needs a clean up
> + * @rc: the RC code of the Destroy Secure Configuration UVC
> + * @rrc: the RRC code of the Destroy Secure Configuration UVC
> + *
> + * Destroy one leftover protected VM.
> + * On success, kvm->mm->context.protected_count will be decremented atomically
> + * and all other resources used by the VM will be freed.
> + *
> + * Return: 0 in case of success, otherwise 1
> + */
> +static int kvm_s390_pv_dispose_one_leftover(struct kvm *kvm,
> +					    struct pv_vm_to_be_destroyed *leftover,
> +					    u16 *rc, u16 *rrc)
>   {
>   	int cc;
>   
> -	cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
> -			   UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
> -	WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);
> +	cc = uv_cmd_nodata(leftover->handle, UVC_CMD_DESTROY_SEC_CONF, rc, rrc); > +	KVM_UV_EVENT(kvm, 3, "PROTVIRT DESTROY LEFTOVER VM: rc %x rrc %x", 
*rc, *rrc);
> +	WARN_ONCE(cc, "protvirt destroy leftover vm failed rc %x rrc %x", *rc, *rrc);
> +	if (cc)
> +		return cc;
maybe set the handle to zero here to be extra sure.
`leftover` will get free'd directly after this function,
but that might change and I assume we do not want to end up with
invalid handles hanging arround.
>   	/*
> -	 * if the mm still has a mapping, make all its pages accessible
> -	 * before destroying the guest
> +	 * 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.
>   	 */
> -	if (mmget_not_zero(kvm->mm)) {
> -		s390_uv_destroy_range(kvm->mm, 0, TASK_SIZE);
> -		mmput(kvm->mm);
> +	free_pages(leftover->stor_base, get_order(uv_info.guest_base_stor_len));
> +	free_pages(leftover->old_gmap_table, CRST_ALLOC_ORDER);
> +	vfree(leftover->stor_var);
> +	atomic_dec(&kvm->mm->context.protected_count);
> +	return 0;
> +}
> +
> +/**
> + * kvm_s390_destroy_lower_2g - Destroy the first 2GB of protected guest memory.
> + * @kvm: the VM whose memory is to be cleared.
> + *
> + * Destroy the first 2GB of guest memory, to avoid prefix issues after reboot.
> + * The CPUs of the protected VM need to be destroyed beforehand.
> + */
> +static void kvm_s390_destroy_lower_2g(struct kvm *kvm)
> +{
> +	const unsigned long pages_2g = SZ_2G / PAGE_SIZE;
> +	struct kvm_memory_slot *slot;
> +	unsigned long len;
> +	int srcu_idx;
> +
> +	srcu_idx = srcu_read_lock(&kvm->srcu);
> +
> +	/* Take the memslot containing guest absolute address 0 */
> +	slot = gfn_to_memslot(kvm, 0);
> +	/* Clear all slots or parts thereof that are below 2GB */
> +	while (slot && slot->base_gfn < pages_2g) {
> +		len = min_t(u64, slot->npages, pages_2g - slot->base_gfn) * PAGE_SIZE;
> +		s390_uv_destroy_range(kvm->mm, slot->userspace_addr, slot->userspace_addr + len);
> +		/* Take the next memslot */
> +		slot = gfn_to_memslot(kvm, slot->base_gfn + slot->npages);
> +	}
> +
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> +}
> +
> +/**
> + * kvm_s390_pv_set_aside - Set aside a protected VM for later teardown.
> + * @kvm: the VM
> + * @rc: return value for the RC field of the UVCB
> + * @rrc: return value for the RRC field of the UVCB
> + *
> + * Set aside the protected VM for a subsequent teardown. The VM will be able
> + * to continue immediately as a non-secure VM, and the information needed to
> + * properly tear down the protected VM is set aside. If another protected VM
> + * was already set aside without starting its teardown, this function will
> + * fail.
> + * The CPUs of the protected VM need to be destroyed beforehand.
> + *
> + * Context: kvm->lock needs to be held
> + *
> + * Return: 0 in case of success, -EINVAL if another protected VM was already set
> + * aside, -ENOMEM if the system ran out of memory.
> + */
> +int kvm_s390_pv_set_aside(struct kvm *kvm, u16 *rc, u16 *rrc)
> +{
> +	struct pv_vm_to_be_destroyed *priv;
> +
> +	/*
> +	 * If another protected VM was already prepared for teardown, refuse.
> +	 * A normal deinitialization has to be performed instead.
> +	 */
> +	if (kvm->arch.pv.set_aside)
> +		return -EINVAL;
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->stor_var = kvm->arch.pv.stor_var;
> +	priv->stor_base = kvm->arch.pv.stor_base;
> +	priv->handle = kvm_s390_pv_get_handle(kvm);
> +	priv->old_gmap_table = (unsigned long)kvm->arch.gmap->table;
> +	WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);
> +	if (s390_replace_asce(kvm->arch.gmap)) {
> +		kfree(priv);
> +		return -ENOMEM;
>   	}
>   
> +	kvm_s390_destroy_lower_2g(kvm);
> +	kvm_s390_clear_pv_state(kvm);
> +	kvm->arch.pv.set_aside = priv;
> +
> +	*rc = UVC_RC_EXECUTED;
> +	*rrc = 42;
> +	return 0;
> +}
> +
> +/**
> + * kvm_s390_pv_deinit_vm - Deinitialize the current protected VM
> + * @kvm: the KVM whose protected VM needs to be deinitialized
> + * @rc: the RC code of the UVC
> + * @rrc: the RRC code of the UVC
> + *
> + * Deinitialize the current protected VM. This function will destroy and
> + * cleanup the current protected VM, but it will not cleanup the guest
> + * memory. This function should only be called when the protected VM has
> + * just been created and therefore does not have any guest memory, or when
> + * the caller cleans up the guest memory separately.
> + *
> + * This function should not fail, but if it does, the donated memory must
> + * not be freed.
> + *
> + * Context: kvm->lock needs to be held
> + *
> + * Return: 0 in case of success, otherwise -EIO
> + */
> +int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
> +{
> +	int cc;
> +
> +	cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
> +			   UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
> +	WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);
>   	if (!cc) {
>   		atomic_dec(&kvm->mm->context.protected_count);
>   		kvm_s390_pv_dealloc_vm(kvm);
> @@ -189,6 +338,127 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>   	return cc ? -EIO : 0;
>   }
>   
> +/**
> + * kvm_s390_pv_deinit_cleanup_all - Clean up all protected VMs associated
> + * with a specific KVM.
> + * @kvm: the KVM to be cleaned up
> + * @rc: the RC code of the first failing UVC
> + * @rrc: the RRC code of the first failing UVC
> + *
> + * This function will clean up all protected VMs associated with a KVM.
> + * This includes the active one, the one prepared for deinitialization with
> + * kvm_s390_pv_set_aside, and any still pending in the need_cleanup list.
> + *
> + * Context: kvm->lock needs to be held unless being called from
> + * kvm_arch_destroy_vm.
> + *
> + * Return: 0 if all VMs are successfully cleaned up, otherwise -EIO
> + */
> +int kvm_s390_pv_deinit_cleanup_all(struct kvm *kvm, u16 *rc, u16 *rrc)
> +{
> +	struct pv_vm_to_be_destroyed *cur;
> +	bool need_zap = false;
> +	u16 _rc, _rrc;
> +	int cc = 0;
> +
> +	/* Make sure the counter does not reach 0 before calling s390_uv_destroy_range */
> +	atomic_inc(&kvm->mm->context.protected_count);
> +
> +	*rc = 1;
> +	/* If the current VM is protected, destroy it */
> +	if (kvm_s390_pv_get_handle(kvm)) {
> +		cc = kvm_s390_pv_deinit_vm(kvm, rc, rrc);
> +		need_zap = true;
> +	}
> +
> +	/* If a previous protected VM was set aside, put it in the need_cleanup list */
> +	if (kvm->arch.pv.set_aside) {
> +		list_add(kvm->arch.pv.set_aside, &kvm->arch.pv.need_cleanup);
> +		kvm->arch.pv.set_aside = NULL;
> +	}
> +
> +	/* Cleanup all protected VMs in the need_cleanup list */
> +	while (!list_empty(&kvm->arch.pv.need_cleanup)) {
> +		cur = list_first_entry(&kvm->arch.pv.need_cleanup, typeof(*cur), list);
> +		need_zap = true;
> +		if (kvm_s390_pv_dispose_one_leftover(kvm, cur, &_rc, &_rrc)) {
> +			cc = 1;
> +			/* do not overwrite a previous error code */
use UVC_RC_EXECUTED
> +			if (*rc == 1) {
> +				*rc = _rc;
> +				*rrc = _rrc;
> +			}
> +		}
> +		list_del(&cur->list);
> +		kfree(cur);
> +	}
> +
> +	/*
> +	 * If the mm still has a mapping, try to mark all its pages as
> +	 * accessible. The counter should not reach zero before this
> +	 * cleanup has been performed.
> +	 */
> +	if (need_zap && mmget_not_zero(kvm->mm)) {
> +		s390_uv_destroy_range(kvm->mm, 0, TASK_SIZE);
> +		mmput(kvm->mm);
> +	}
> +
> +	/* Now the counter can safely reach 0 */
> +	atomic_dec(&kvm->mm->context.protected_count);
> +	return cc ? -EIO : 0;
> +}
> +
> +/**
> + * kvm_s390_pv_deinit_aside_vm - Teardown a previously set aside protected VM.
> + * @kvm the VM previously associated with the protected VM
> + * @rc return value for the RC field of the UVCB
> + * @rrc return value for the RRC field of the UVCB
> + *
> + * Tear down the protected VM that had been previously prepared for teardown
> + * using kvm_s390_pv_set_aside_vm. Ideally this should be called by
> + * userspace asynchronously from a separate thread.
> + *
> + * Context: kvm->lock must not be held.
> + *
> + * Return: 0 in case of success, -EINVAL if no protected VM had been
> + * prepared for asynchronous teardowm, -EIO in case of other errors.
> + */
> +int kvm_s390_pv_deinit_aside_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
> +{
> +	struct pv_vm_to_be_destroyed *p;
> +	int ret = 0;
> +
> +	lockdep_assert_not_held(&kvm->lock);
> +	mutex_lock(&kvm->lock);
> +	p = kvm->arch.pv.set_aside;
> +	kvm->arch.pv.set_aside = NULL;
> +	mutex_unlock(&kvm->lock);
> +	if (!p)
> +		return -EINVAL;
> +
> +	/* When a fatal signal is received, stop immediately */
> +	if (s390_uv_destroy_range_interruptible(kvm->mm, 0, TASK_SIZE_MAX))
> +		goto done;
> +	if (kvm_s390_pv_dispose_one_leftover(kvm, p, rc, rrc))
> +		ret = -EIO;
> +	kfree(p);
> +	p = NULL;
> +done:
> +	/*
> +	 * p is not NULL if we aborted because of a fatal signal, in which
> +	 * case queue the leftover for later cleanup.
> +	 */
> +	if (p) {
> +		mutex_lock(&kvm->lock);
> +		list_add(&p->list, &kvm->arch.pv.need_cleanup);
> +		mutex_unlock(&kvm->lock);
> +		/* Did not finish, but pretend things went well */
use UVC_RC_EXECUTED
> +		*rc = 1;
> +		*rrc = 42;
> +	}
> +	return ret;
> +}
> +
>   static void kvm_s390_pv_mmu_notifier_release(struct mmu_notifier *subscription,
>   					     struct mm_struct *mm)
>   {
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index eed0315a77a6..02602c5c1975 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1739,6 +1739,8 @@ enum pv_cmd_id {
>   	KVM_PV_UNSHARE_ALL,
>   	KVM_PV_INFO,
>   	KVM_PV_DUMP,
> +	KVM_PV_ASYNC_CLEANUP_PREPARE,
> +	KVM_PV_ASYNC_CLEANUP_PERFORM,
>   };
>   
>   struct kvm_pv_cmd {

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