linux-kernel - Re: [PATCH v10 14/50] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP

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Message-ID: <20231206170807.GBZXCqd0z8uu2rlhpn@fat_crate.local>
Date:   Wed, 6 Dec 2023 18:08:07 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kalra, Ashish" <ashish.kalra@....com>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
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        jarkko@...nel.org, nikunj.dadhania@....com, pankaj.gupta@....com,
        liam.merwick@...cle.com, zhi.a.wang@...el.com,
        Brijesh Singh <brijesh.singh@....com>,
        Jarkko Sakkinen <jarkko@...fian.com>
Subject: Re: [PATCH v10 14/50] crypto: ccp: Add support to initialize the
 AMD-SP for SEV-SNP

On Wed, Nov 29, 2023 at 08:13:52PM -0600, Kalra, Ashish wrote:
> It surely seems hard to follow up, so i am anyway going to clean it up by:
> 
> Adding the "probe" parameter to sev_platform_init() where the parameter
> being true indicates that we only want to do SNP initialization on probe,
> the same parameter will get passed on to
> __sev_platform_init_locked().

That's exactly what you should *not* do - the probe parameter controls
whether

	if (psp_init_on_probe)
		__sev_platform_init_locked(error);

and so on should get executed or not.

If it is unclear, lemme know and I'll do a diff to show you what I mean.
	
> > > +	/* Prepare for first SNP guest launch after INIT */
> > > +	wbinvd_on_all_cpus();
> > 
> > Why is that WBINVD needed?
> 
> As the comment above mentions, WBINVD + DF_FLUSH is needed before the first
> guest launch.

Lemme see if I get this straight. The correct order is:

	WBINVD
	SNP_INIT_*
	WBINVD
	DF_FLUSH

If so, do a comment which goes like this:

	/*
	 * The order of commands to execute before the first guest
	 * launch is the following:
	 *
	 * bla...
	 */


> In the latest code base, _sev_snp_shutdown_locked() is called from
> __sev_firmware_shutdown().

Then carve that function out only when needed - do not do changes
preemptively. This is not helping during review.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette