linux-kernel - Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for SNP_{GET, GET_EXT}

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Date:   Mon, 14 Aug 2023 09:25:06 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>
CC:     <linux-coco@...ts.linux.dev>, Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        "Brijesh Singh" <brijesh.singh@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for
 SNP_{GET, GET_EXT}_REPORT

Peter Zijlstra wrote:
> On Mon, Aug 14, 2023 at 12:43:38AM -0700, Dan Williams wrote:
> > +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
> 
> > +			  size_t *outblob_len)
> > +{
> 
> > +
> > +	u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
> > +
> 
> > +
> > +	*outblob_len = size;
> > +	no_free_ptr(buf);
> > +	return buf;
> 
> This seems broken, no_free_ptr(x) is basically xchg(X, NULL) (except no
> atomics). So the above would end up being:
> 
> 	return NULL;
> 
> What you want to write is somehting like:
> 
> 	return no_free_ptr(buf);
> 
> or, a convenient shorthand:
> 
> 	return_ptr(buf);
> 

Oh, I indeed did not realize that no_free_ptr() had side effects beyond
canceling the free when the variable goes out of scope. Will switch to
return_ptr().