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X-CSE-ConnectionGUID: 3D+JbRTsTDW04zolJJ5SlQ== X-CSE-MsgGUID: cINeZdSGS6m67R6dEiIJuA== X-IronPort-AV: E=McAfee;i="6700,10204,11441"; a="50009251" X-IronPort-AV: E=Sophos;i="6.15,309,1739865600"; d="scan'208";a="50009251" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 May 2025 10:29:49 -0700 X-CSE-ConnectionGUID: PqTrVVY7SsqG0j33D4snSw== X-CSE-MsgGUID: 60OZtcGTTyOGheO66+8wWw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,309,1739865600"; d="scan'208";a="146204841" Received: from msatwood-mobl.amr.corp.intel.com (HELO [10.125.109.147]) ([10.125.109.147]) by orviesa004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 May 2025 10:29:49 -0700 Message-ID: Date: Fri, 23 May 2025 10:29:48 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/5] KVM: SEV: Add SEV-SNP CipherTextHiding support To: Ashish Kalra , corbet@lwn.net, seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, herbert@gondor.apana.org.au, akpm@linux-foundation.org, paulmck@kernel.org, rostedt@goodmis.org Cc: x86@kernel.org, thuth@redhat.com, ardb@kernel.org, gregkh@linuxfoundation.org, john.allen@amd.com, davem@davemloft.net, thomas.lendacky@amd.com, michael.roth@amd.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-doc@vger.kernel.org References: From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/19/25 17:02, Ashish Kalra wrote: > + kvm-amd.ciphertext_hiding_nr_asids= > + [KVM,AMD] Enables SEV-SNP CipherTextHiding feature and > + controls show many ASIDs are available for SEV-SNP guests. > + The ASID space is basically split into legacy SEV and > + SEV-ES+. CipherTextHiding feature further splits the > + SEV-ES+ ASID space into SEV-ES and SEV-SNP. > + If the value is -1, then it is used as an auto flag > + and splits the ASID space equally between SEV-ES and > + SEV-SNP ASIDs. This help text isn't great. It doesn't come out and say what the connection between CipherTextHiding and SEV-ES+. It's also impossible to choose a good number without knowing how large the ASID space is in the first place. Why use "-1"? Why not just take "auto" as a parameter? It also needs to say what CipherTextHiding is in the first place and be more clear about what the tradeoffs are from enabling this.