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

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Date: Sun, 31 Dec 2023 10:44:40 -0600
From: Michael Roth <michael.roth@....com>
To: Borislav Petkov <bp@...en8.de>
CC: <x86@...nel.org>, <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
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	Brijesh Singh <brijesh.singh@....com>, Jarkko Sakkinen <jarkko@...fian.com>
Subject: Re: [PATCH v1 01/26] x86/cpufeatures: Add SEV-SNP CPU feature

On Sun, Dec 31, 2023 at 12:50:12PM +0100, Borislav Petkov wrote:
> 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

Sorry, I must have inverted things when I was squashing in the changes =\

I've gone ahead and force-pushed your fixup to the snp-host-init-v1
branch.

Thanks,

Mike

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette