Re: [PATCH v5 2/6] KVM: s390: pci: Fix memory accounting for pinned/unpinned pages

[Matthew Rosato]

On 7/23/26 2:34 PM, Farhan Ali wrote:
> The account_mem() and unaccount_mem() functions call get_uid() which
> increments the reference count of struct user_struct on every invocation.
> But we don't decrement the count by calling free_uid(). It also
> accounted/unaccounted the pages against the current->mm. But its possible
> the unaccount_mem() can be called from a different process context than the
> one that originally pinned the pages.
> 
> Let's fix this by storing the pinning process user_struct and mm_struct
> when accounting for pinned pages, and subsequently free these resources
> when the pages are unpinned.
> 
> Fixes: 3c5a1b6f0a18 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
> Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>

Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>

With one note below:


>  
>  static int kvm_s390_pci_aif_enable(struct zpci_dev *zdev, struct zpci_fib *fib,
> @@ -279,7 +300,7 @@ static int kvm_s390_pci_aif_enable(struct zpci_dev *zdev, struct zpci_fib *fib,
>  	}
>  
>  	/* Account for pinned pages, roll back on failure */
> -	if (account_mem(pcount))
> +	if (account_mem(zdev->kzdev, pcount))
>  		goto unpin2;
>  

Sashiko marked a failure to unaccount on error paths after this point as
a regression, but it's a pre-existing issue AND resolved with patch 3 of
this series.

>  	/* AISB must be allocated before we can fill in GAITE */
> @@ -400,7 +421,7 @@ static int kvm_s390_pci_aif_disable(struct zpci_dev *zdev, bool force)
>  		pcount++;
>  	}
>  	if (pcount > 0)
> -		unaccount_mem(pcount);
> +		unaccount_mem(kzdev, pcount);
>  out:
>  	mutex_unlock(&aift->aift_lock);
>  
> diff --git a/arch/s390/kvm/pci.h b/arch/s390/kvm/pci.h
> index ff0972dd5e71..fdf8c7bf4ed0 100644
> --- a/arch/s390/kvm/pci.h
> +++ b/arch/s390/kvm/pci.h
> @@ -22,6 +22,8 @@ struct kvm_zdev {
>  	struct kvm *kvm;
>  	struct zpci_fib fib;
>  	struct list_head entry;
> +	struct user_struct *user_account;
> +	struct mm_struct *mm_account;
>  };
>  
>  struct zpci_gaite {