linux-kernel - Re: [PATCH v16 2/3] virt: Add TDX guest driver

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Date:   Tue, 1 Nov 2022 10:33:59 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v16 2/3] virt: Add TDX guest driver

On Sun, Oct 30, 2022 at 07:53:19AM +0100, Greg Kroah-Hartman wrote:
> On Sat, Oct 29, 2022 at 04:17:39PM -0700, Sathyanarayanan Kuppuswamy wrote:
> > Hi Greg
> > 
> > On 10/27/22 11:25 PM, Greg Kroah-Hartman wrote:
> > > On Thu, Oct 27, 2022 at 05:28:19PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > 
> > >> +
> > >> +static long tdx_guest_ioctl(struct file *file, unsigned int cmd,
> > >> +			    unsigned long arg)
> > >> +{
> > >> +	switch (cmd) {
> > >> +	case TDX_CMD_GET_REPORT:
> > >> +		return tdx_get_report((void __user *)arg);
> > > 
> > > You know the type of this pointer here, why not cast it instead of
> > > having to cast it from void * again?
> > 
> > The only place we use arg pointer is in copy_from_user() function,
> > which expects void __user * pointer. So why cast it as struct
> > tdx_report_req * here?
> 
> Because then your function will show the true type and you don't have to
> cast it again.
> 

If we are taking this route, isn't better to move the copy_from_user
call to tdx_guest_ioctl and pass the resulting struct tdx_report_req
pointer to tdx_get_report?