Message-ID: <aKBPjfyIHMc2X_ZL@gondor.apana.org.au>
Date: Sat, 16 Aug 2025 17:29:49 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: corbet@....net, seanjc@...gle.com, pbonzini@...hat.com,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	thomas.lendacky@....com, john.allen@....com, davem@...emloft.net,
	akpm@...ux-foundation.org, rostedt@...dmis.org, paulmck@...nel.org,
	nikunj@....com, Neeraj.Upadhyay@....com, aik@....com,
	ardb@...nel.org, michael.roth@....com, arnd@...db.de,
	linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v7 0/7] Add SEV-SNP CipherTextHiding feature support

On Mon, Jul 21, 2025 at 02:12:15PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> Ciphertext hiding prevents host accesses from reading the ciphertext
> of SNP guest private memory. Instead of reading ciphertext, the host
> will see constant default values (0xff).
> 
> The SEV ASID space is split into SEV and SEV-ES/SNP ASID ranges.
> Enabling ciphertext hiding further splits the SEV-ES/SEV-SNP ASID space
> into separate ASID ranges for SEV-ES and SEV-SNP guests.
> 
> Add new module parameter to the KVM module to enable ciphertext hiding
> support and a user configurable system-wide maximum SNP ASID value. If
> the module parameter value is "max" then the complete SEV-ES/SEV-SNP
> space is allocated to SEV-SNP guests.
> 
> v7:
> - Fix comments.
> - Move the check for module parameter ciphertext_hiding_asids inside
> check_and_enable_sev_snp_ciphertext_hiding(), this keeps all the logic
> related to the parameter in a single function.
> 
> v6:
> - Fix module parameter ciphertext_hiding_asids=0 case.
> - Coalesce multiple cases of handling invalid module parameter
> ciphertext_hiding_asids into a single branch/label.
> - Fix commit logs.
> - Fix Documentation.
> 
> v5:
> - Add pre-patch to cache SEV platform status and use this cached
> information to set api_major/api_minor/build.
> - Since the SEV platform status and SNP platform status differ, 
> remove the state field from sev_device structure and instead track
> SEV platform state from cached SEV platform status.
> - If SNP is enabled then cached SNP platform status is used for 
> api_major/api_minor/build.
> - Fix using sev_do_cmd() instead of __sev_do_cmd_locked().
> - Fix commit logs.
> - Fix kernel-parameters documentation. 
> - Modify KVM module parameter to enable CipherTextHiding to support
> "max" option to allow complete SEV-ES+ ASID space to be allocated
> to SEV-SNP guests.
> - Do not enable ciphertext hiding if module parameter to specify
> maximum SNP ASID is invalid.
> 
> v4:
> - Fix buffer allocation for SNP_FEATURE_INFO command to correctly
> handle page boundary check requirements.
> - Return correct length for SNP_FEATURE_INFO command from
> sev_cmd_buffer_len().
> - Switch to using SNP platform status instead of SEV platform status if
> SNP is enabled and cache SNP platform status and feature information.
> Modify sev_get_api_version() accordingly.
> - Fix commit logs.
> - Expand the comments on why both the feature info and the platform
> status fields have to be checked for CipherTextHiding feature 
> detection and enablement.
> - Add new preperation patch for CipherTextHiding feature which
> introduces new {min,max}_{sev_es,snp}_asid variables along with
> existing {min,max}_sev_asid variable to simplify partitioning of the
> SEV and SEV-ES+ ASID space.
> - Switch to single KVM module parameter to enable CipherTextHiding
> feature and the maximum SNP ASID usable for SNP guests when 
> CipherTextHiding feature is enabled.
> 
> v3:
> - rebase to linux-next.
> - rebase on top of support to move SEV-SNP initialization to
> KVM module from CCP driver.
> - Split CipherTextHiding support between CCP driver and KVM module
> with KVM module calling into CCP driver to initialize SNP with
> CipherTextHiding enabled and MAX ASID usable for SNP guest if
> KVM is enabling CipherTextHiding feature.
> - Move module parameters to enable CipherTextHiding feature and
> MAX ASID usable for SNP guests from CCP driver to KVM module
> which allows KVM to be responsible for enabling CipherTextHiding
> feature if end-user requests it.
> 
> v2:
> - Fix and add more description to commit logs.
> - Rename sev_cache_snp_platform_status_and_discover_features() to 
> snp_get_platform_data().
> - Add check in snp_get_platform_data to guard against being called
> after SNP_INIT_EX.
> - Fix comments for new structure field definitions being added.
> - Fix naming for new structure being added.
> - Add new vm-type parameter to sev_asid_new().
> - Fix identation.
> - Rename CCP module parameters psp_cth_enabled to cipher_text_hiding and 
> psp_max_snp_asid to max_snp_asid.
> - Rename max_snp_asid to snp_max_snp_asid. 
> 
> Ashish Kalra (7):
>   crypto: ccp - New bit-field definitions for SNP_PLATFORM_STATUS
>     command
>   crypto: ccp - Cache SEV platform status and platform state
>   crypto: ccp - Add support for SNP_FEATURE_INFO command
>   crypto: ccp - Introduce new API interface to indicate SEV-SNP
>     Ciphertext hiding feature
>   crypto: ccp - Add support to enable CipherTextHiding on SNP_INIT_EX
>   KVM: SEV: Introduce new min,max sev_es and sev_snp asid variables
>   KVM: SEV: Add SEV-SNP CipherTextHiding support
> 
>  .../admin-guide/kernel-parameters.txt         |  18 +++
>  arch/x86/kvm/svm/sev.c                        |  96 +++++++++++--
>  drivers/crypto/ccp/sev-dev.c                  | 127 ++++++++++++++++--
>  drivers/crypto/ccp/sev-dev.h                  |   6 +-
>  include/linux/psp-sev.h                       |  44 +++++-
>  include/uapi/linux/psp-sev.h                  |  10 +-
>  6 files changed, 274 insertions(+), 27 deletions(-)
> 
> -- 
> 2.34.1

Patches 1-5 applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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