linux-kernel - Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

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Message-ID: <20231220070703.24rfvmjegrvozkfr@amd.com>
Date: Wed, 20 Dec 2023 01:07:03 -0600
From: Michael Roth <michael.roth@....com>
To: Borislav Petkov <bp@...en8.de>
CC: <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
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	<pankaj.gupta@....com>, <liam.merwick@...cle.com>, <zhi.a.wang@...el.com>,
	Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization
 support

On Tue, Nov 07, 2023 at 05:31:42PM +0100, Borislav Petkov wrote:
> On Mon, Oct 16, 2023 at 08:27:35AM -0500, Michael Roth wrote:
> > +static bool early_rmptable_check(void)
> > +{
> > +	u64 rmp_base, rmp_size;
> > +
> > +	/*
> > +	 * For early BSP initialization, max_pfn won't be set up yet, wait until
> > +	 * it is set before performing the RMP table calculations.
> > +	 */
> > +	if (!max_pfn)
> > +		return true;
> 
> This already says that this is called at the wrong point during init.
> 
> Right now we have
> 
> early_identify_cpu -> early_init_amd -> early_detect_mem_encrypt
> 
> which runs only on the BSP but then early_init_amd() is called in
> init_amd() too so that it takes care of the APs too.
> 
> Which ends up doing a lot of unnecessary work on each AP in
> early_detect_mem_encrypt() like calculating the RMP size on each AP
> unnecessarily where this needs to happen exactly once.
> 
> Is there any reason why this function cannot be moved to init_amd()
> where it'll do the normal, per-AP init?
> 
> And the stuff that needs to happen once, needs to be called once too.

I've renamed/repurposed snp_get_rmptable_info() to
snp_probe_rmptable_info(). It now reads the MSRs, sanity-checks them,
and stores the values into ro_after_init variables on success.

Subsequent code uses those values to initialize the RMP table mapping
instead of re-reading the MSRs.

I've moved the call-site for snp_probe_rmptable_info() to
bsp_init_amd(), which gets called right after early_init_amd(), so
should still be early enough to clear X86_FEATURE_SEV_SNP such that
AutoIBRS doesn't get disabled if SNP isn't available on the system. APs
don't call bsp_init_amd(), so that should avoid doing multiple MSR reads.

And I think Ashish has all the other review comments addressed now.

Thanks,

Mike