linux-kernel - Re: [PATCH v7 01/45] x86/compressed/64: detect/setup SEV/SME features earlier in boot

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Message-ID: <20211112203001.kdzhpgp3uqcr2dy5@amd.com>
Date:   Fri, 12 Nov 2021 14:30:01 -0600
From:   Michael Roth <michael.roth@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Brijesh Singh <brijesh.singh@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <linux-efi@...r.kernel.org>, <platform-driver-x86@...r.kernel.org>,
        <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Vitaly Kuznetsov" <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        <tony.luck@...el.com>, <marcorr@...gle.com>,
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v7 01/45] x86/compressed/64: detect/setup SEV/SME
 features earlier in boot

On Fri, Nov 12, 2021 at 05:52:51PM +0100, Borislav Petkov wrote:
> On Wed, Nov 10, 2021 at 04:06:47PM -0600, Brijesh Singh wrote:
> > +void sev_enable(struct boot_params *bp)
> > +{
> > +	unsigned int eax, ebx, ecx, edx;
> > +
> > +	/* Check for the SME/SEV support leaf */
> > +	eax = 0x80000000;
> > +	ecx = 0;
> > +	native_cpuid(&eax, &ebx, &ecx, &edx);
> > +	if (eax < 0x8000001f)
> > +		return;
> > +
> > +	/*
> > +	 * Check for the SME/SEV feature:
> > +	 *   CPUID Fn8000_001F[EAX]
> > +	 *   - Bit 0 - Secure Memory Encryption support
> > +	 *   - Bit 1 - Secure Encrypted Virtualization support
> > +	 *   CPUID Fn8000_001F[EBX]
> > +	 *   - Bits 5:0 - Pagetable bit position used to indicate encryption
> > +	 */
> > +	eax = 0x8000001f;
> > +	ecx = 0;
> > +	native_cpuid(&eax, &ebx, &ecx, &edx);
> > +	/* Check whether SEV is supported */
> > +	if (!(eax & BIT(1)))
> > +		return;
> > +
> > +	/* Check the SEV MSR whether SEV or SME is enabled */
> > +	sev_status   = rd_sev_status_msr();
> > +
> > +	if (!(sev_status & MSR_AMD64_SEV_ENABLED))
> > +		error("SEV support indicated by CPUID, but not SEV status MSR.");
> 
> What is the practical purpose of this test?

In the current QEMU/KVM implementation the SEV* CPUID bits are only
exposed for SEV guests, so this was more of a sanity check on that. But
looking at things more closely: that's more of a VMM-specific behavior
and isn't necessarily an invalid guest configuration as far as the spec
is concerned, so I think this check should be dropped.

> 
> > +	sme_me_mask = 1UL << (ebx & 0x3f);
> 
> 	sme_me_mask = BIT_ULL(ebx & 0x3f);

Will do.

Thanks,

Mike

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
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