linux-kernel - Re: [PATCH v14 1/3] x86/tdx: Make __tdx_module

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Date:   Wed, 12 Oct 2022 19:26:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        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>,
        Wander Lairson Costa <wander@...hat.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 v14 1/3] x86/tdx: Make __tdx_module_call() usable in
 driver module

On Wed, Oct 12, 2022 at 10:13:50AM -0700, Sathyanarayanan Kuppuswamy wrote:
> Hi,
> 
> On 10/12/22 9:23 AM, Greg Kroah-Hartman wrote:
> > On Wed, Oct 12, 2022 at 08:44:04AM -0700, Sathyanarayanan Kuppuswamy wrote:
> >>
> >>
> >> On 10/12/22 7:27 AM, Borislav Petkov wrote:
> >>> On Wed, Oct 12, 2022 at 06:35:56AM -0700, Sathyanarayanan Kuppuswamy wrote:
> >>>> So we should create a new wrapper for this use case or use
> >>>
> >>> Yes, you got it - a new wrapper pls.
> >>
> >> Ok. I will add a new wrapper to get the TDREPORT. 
> >>
> >> +/*
> >>
> >> + * Add a wrapper for TDG.MR.REPORT TDCALL. It is used in TDX guest
> >>
> >> + * driver module to get the TDREPORT.
> >>
> >> + */
> >>
> >> +long tdx_mcall_get_report(void *reportdata, void *tdreport, u8 subtype)
> > 
> > Why "long"?
> 
> We used long because __tdx_module_call() call returns u64 value.

Great, then use u64 please.  Or if you are returning negative errors,
use s64 to be specific.

> Alternatively, we can also check for return value of __tdx_module_call() here
> and return 0/-EIO as return values. In this case we can change return value
> to int.

That would make more sense, right?

> > 
> > Why void *?  Don't you have real types for these?
> 
> We use these buffers as an intermediary to transfer data between userspace and
> the TDX module. In the kernel we don't consume these datas. So we did not define
> the type of the data.

Then these are userspace pointers?  Why are they not marked as such?

thanks,

greg k-h