linux-kernel - Re: [PATCH v1 01/26] x86/cpufeatures: Add SEV-SNP CPU feature

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Date: Sun, 31 Dec 2023 12:50:12 +0100
From: Borislav Petkov <bp@...en8.de>
To: Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-mm@...ck.org, linux-crypto@...r.kernel.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,
	rientjes@...gle.com, tobin@....com, vbabka@...e.cz,
	kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
	jarkko@...nel.org, ashish.kalra@....com, 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 v1 01/26] x86/cpufeatures: Add SEV-SNP CPU feature

On Sat, Dec 30, 2023 at 10:19:29AM -0600, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@....com>
> 
> Add CPU feature detection for Secure Encrypted Virtualization with
> Secure Nested Paging. This feature adds a strong memory integrity
> protection to help prevent malicious hypervisor-based attacks like
> data replay, memory re-mapping, and more.
> 
> Since enabling the SNP CPU feature imposes a number of additional
> requirements on host initialization and handling legacy firmware APIs
> for SEV/SEV-ES guests, only introduce the CPU feature bit so that the
> relevant handling can be added, but leave it disabled via a
> disabled-features mask.
> 
> Once all the necessary changes needed to maintain legacy SEV/SEV-ES
> support are introduced in subsequent patches, the SNP feature bit will
> be unmasked/enabled.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Jarkko Sakkinen <jarkko@...fian.com>
> Signed-off-by: Ashish Kalra <Ashish.Kalra@....com>
> Signed-off-by: Michael Roth <michael.roth@....com>
> ---
>  arch/x86/include/asm/cpufeatures.h       | 1 +
>  arch/x86/include/asm/disabled-features.h | 4 +++-
>  arch/x86/kernel/cpu/amd.c                | 5 +++--
>  tools/arch/x86/include/asm/cpufeatures.h | 1 +
>  4 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 29cb275a219d..9492dcad560d 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -442,6 +442,7 @@
>  #define X86_FEATURE_SEV			(19*32+ 1) /* AMD Secure Encrypted Virtualization */
>  #define X86_FEATURE_VM_PAGE_FLUSH	(19*32+ 2) /* "" VM Page Flush MSR is supported */
>  #define X86_FEATURE_SEV_ES		(19*32+ 3) /* AMD Secure Encrypted Virtualization - Encrypted State */
> +#define X86_FEATURE_SEV_SNP		(19*32+ 4) /* AMD Secure Encrypted Virtualization - Secure Nested Paging */
>  #define X86_FEATURE_V_TSC_AUX		(19*32+ 9) /* "" Virtual TSC_AUX */
>  #define X86_FEATURE_SME_COHERENT	(19*32+10) /* "" AMD hardware-enforced cache coherency */
>  #define X86_FEATURE_DEBUG_SWAP		(19*32+14) /* AMD SEV-ES full debug state swap support */
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 702d93fdd10e..a864a5b208fa 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -117,6 +117,8 @@
>  #define DISABLE_IBT	(1 << (X86_FEATURE_IBT & 31))
>  #endif
>  
> +#define DISABLE_SEV_SNP		0

I think you want this here if SEV_SNP should be initially disabled:

diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index a864a5b208fa..5b2fab8ad262 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -117,7 +117,7 @@
 #define DISABLE_IBT	(1 << (X86_FEATURE_IBT & 31))
 #endif
 
-#define DISABLE_SEV_SNP		0
+#define DISABLE_SEV_SNP	(1 << (X86_FEATURE_SEV_SNP & 31))
 
 /*
  * Make sure to add features to the correct mask

-- 
Regards/Gruss,
    Boris.

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