Re: [PATCH v3 03/18] KVM: PPC: Account TCE pages in locked_vm

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2014-07-24 at 18:47 +1000, Alexey Kardashevskiy wrote:
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---

You need a description.

>  arch/powerpc/kvm/book3s_64_vio.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index 516f2ee..48b7ed4 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -45,18 +45,48 @@ static long kvmppc_stt_npages(unsigned long window_size)
>  		     * sizeof(u64), PAGE_SIZE) / PAGE_SIZE;
>  }
>  
> +/*
> + * Checks ulimit in order not to let the user space to pin all
> + * available memory for TCE tables.
> + */
> +static long kvmppc_account_memlimit(long npages)
> +{
> +	unsigned long ret = 0, locked, lock_limit;
> +
> +	if (!current->mm)
> +		return -ESRCH; /* process exited */
> +
> +	down_write(&current->mm->mmap_sem);
> +	locked = current->mm->locked_vm + npages;
> +	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +	if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
> +		pr_warn("RLIMIT_MEMLOCK (%ld) exceeded\n",
> +				rlimit(RLIMIT_MEMLOCK));
> +		ret = -ENOMEM;
> +	} else {
> +		current->mm->locked_vm += npages;
> +	}
> +	up_write(&current->mm->mmap_sem);
> +
> +	return ret;
> +}
> +
>  static void release_spapr_tce_table(struct kvmppc_spapr_tce_table *stt)
>  {
>  	struct kvm *kvm = stt->kvm;
>  	int i;
> +	long npages = kvmppc_stt_npages(stt->window_size);
>  
>  	mutex_lock(&kvm->lock);
>  	list_del(&stt->list);
> -	for (i = 0; i < kvmppc_stt_npages(stt->window_size); i++)
> +	for (i = 0; i < npages; i++)
>  		__free_page(stt->pages[i]);
> +
>  	kfree(stt);
>  	mutex_unlock(&kvm->lock);
>  
> +	kvmppc_account_memlimit(-(npages + 1));
> +
>  	kvm_put_kvm(kvm);
>  }
>  
> @@ -112,6 +142,9 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>  	}
>  
>  	npages = kvmppc_stt_npages(args->window_size);
> +	ret = kvmppc_account_memlimit(npages + 1);
> +	if (ret)
> +		goto fail;

This is called for VFIO only or is it also called when creating TCE
tables for emulated devices ? Because in the latter case, you don't
want to account the pages as locked, do you ?

Also, you need to explain what +1

Finally, do I correctly deduce that creating 10 TCE tables of 2G
each will end up accounting 20G as locked even if the guest for
example only has 4G of RAM ? 

>  	stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),
>  		      GFP_KERNEL);

Ben.