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X-IronPort-AV: E=McAfee;i="6600,9927,10955"; a="7354413" X-IronPort-AV: E=Sophos;i="6.05,200,1701158400"; d="scan'208";a="7354413" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2024 12:22:45 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,200,1701158400"; d="scan'208";a="18587250" Received: from aegarcia-mobl1.amr.corp.intel.com (HELO [10.212.31.16]) ([10.212.31.16]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2024 12:22:40 -0800 Message-ID: <011fed12-7fcd-4df8-b264-b55db2f3e95f@intel.com> Date: Tue, 16 Jan 2024 12:22:39 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 11/26] x86/sev: Invalidate pages from the direct map when adding them to the RMP table Content-Language: en-US To: Michael Roth Cc: Tom Lendacky , Borislav Petkov , x86@kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, tobin@ibm.com, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, zhi.a.wang@intel.com, Brijesh Singh , rppt@kernel.org References: <20231230161954.569267-1-michael.roth@amd.com> <20231230161954.569267-12-michael.roth@amd.com> <20240112200751.GHZaGcF0-OZVJiIB7y@fat_crate.local> <63297d29-bb24-ac5e-0b47-35e22bb1a2f8@amd.com> <336b55f9-c7e6-4ec9-806b-cb3659dbfdc3@intel.com> <20240116161909.msbdwiyux7wsxw2i@amd.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C26DC40003 X-Stat-Signature: nx9epgkhkrfqdu1xbuuywakj4b4kgtnu X-Rspam-User: X-HE-Tag: 1705436577-614827 X-HE-Meta: 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 LLAGqyYg RGd75FWZxj5B24nWFMaffedhS2fVr+CRXznj/LJkqcnKmsU1NbLLGhqR+MD2XAIBYnFrJQgOpj9pFcM8N+H4IfEgMPjoljTvvqNQpIrSJf7GqPO97FtWOEmRD5/A38oMuF7JO5+ClSnMtqDkwCCgWg3VYoTpwVPEwqkafenrYmPbUkwPRqbKgxgRNywsSdfPg1ZcnNUbOyVY4vU3LAzPTUc4OY5QAq7v+azv1o8J3X76tBHw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/16/24 08:19, Michael Roth wrote: > > So at the very least, if we went down this path, we would be worth > investigating the following areas in addition to general perf testing: > > 1) Only splitting directmap regions corresponding to kernel-allocatable > *data* (hopefully that's even feasible...) Take a look at the 64-bit memory map in here: https://www.kernel.org/doc/Documentation/x86/x86_64/mm.rst We already have separate mappings for kernel data and (normal) kernel text. > 2) Potentially deferring the split until an SNP guest is actually > run, so there isn't any impact just from having SNP enabled (though > you still take a hit from RMP checks in that case so maybe it's not > worthwhile, but that itself has been noted as a concern for users > so it would be nice to not make things even worse). Yes, this would be nice too. >> Actually, where _is_ the TLB flushing here? > Boris pointed that out in v6, and we implemented it in v7, but it > completely cratered performance: That *desperately* needs to be documented. How can it be safe to skip the TLB flush? It this akin to a page permission promotion where you go from RO->RW but can skip the TLB flush? In that case, the CPU will see the RO TLB entry violation, drop it, and re-walk the page tables, discovering the RW entry. Does something similar happen here where the CPU sees the 2M/4k conflict in the TLB, drops the 2M entry, does a re-walk then picks up the newly-split 2M->4k entries? I can see how something like that would work, but it's _awfully_ subtle to go unmentioned.