linux-kernel - Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device

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Date:   Fri, 13 May 2022 10:37:58 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Steffen Eiden <seiden@...ux.ibm.com>
Cc:     Greg KH <greg@...ah.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Shuah Khan <shuah@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Nico Boehr <nrb@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device

On Fri, 13 May 2022 09:45:39 +0200
Steffen Eiden <seiden@...ux.ibm.com> wrote:

> On 5/12/22 16:33, Claudio Imbrenda wrote:
> 
> [snip]
> 
> >> +/*
> >> + * IOCTL entry point for the Ultravisor device.
> >> + */
> >> +static long uvio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> >> +{
> >> +	void __user *argp = (void __user *)arg;
> >> +	struct uvio_ioctl_cb *uv_ioctl;
> >> +	long ret;
> >> +
> >> +	ret = -ENOMEM;
> >> +	uv_ioctl = vzalloc(sizeof(*uv_ioctl));  
> > struct uvio_ioctl_cb is rather small, couldn't you just allocate it on
> > the stack?
> >   
> IIRC it was on stack in some previous version. We then had a discussion
> earlier about this triggered by the inverse comment and decided to not 
> use the stack.

ok fair enough

but what's the reason for a vzalloc instead of a kzalloc, when the
allocation is surely going to be small?

> 
> [snip]
>