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[192.55.52.151]) by mx.google.com with ESMTPS id w7si185585pgs.168.2019.06.13.09.21.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 09:21:17 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.151 as permitted sender) client-ip=192.55.52.151; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Jun 2019 09:21:16 -0700 X-ExtLoop1: 1 Received: from enagarix-mobl.amr.corp.intel.com (HELO [10.251.15.213]) ([10.251.15.213]) by orsmga004.jf.intel.com with ESMTP; 13 Jun 2019 09:21:16 -0700 Subject: Re: [RFC 00/10] Process-local memory allocations for hiding KVM secrets To: Andy Lutomirski , Alexander Graf , Nadav Amit Cc: Marius Hillenbrand , kvm list , LKML , Kernel Hardening , Linux-MM , Alexander Graf , David Woodhouse , the arch/x86 maintainers , Peter Zijlstra References: <20190612170834.14855-1-mhillenb@amazon.de> <459e2273-bc27-f422-601b-2d6cdaf06f84@amazon.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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: On 6/13/19 9:13 AM, Andy Lutomirski wrote: >> It might make sense to use it for kmap_atomic() for debug purposes, as >> it ensures that other users can no longer access the same mapping >> through the linear map. However, it does come at quite a big cost, as we >> need to shoot down the TLB of all other threads in the system. So I'm >> not sure it's of general value? > What I meant was that kmap_atomic() could use mm-local memory so that > it doesn't need to do a global shootdown. But I guess it's not > actually used for real on 64-bit, so this is mostly moot. Are you > planning to support mm-local on 32-bit? Do we *do* global shootdowns on kmap_atomic()s on 32-bit? I thought we used entirely per-cpu addresses, so a stale entry from another CPU can get loaded in the TLB speculatively but it won't ever actually get used. I think it goes: kunmap_atomic() -> __kunmap_atomic() -> kpte_clear_flush() -> __flush_tlb_one_kernel() -> __flush_tlb_one_user() -> __native_flush_tlb_one_user() -> invlpg The per-cpu address calculation is visible in kmap_atomic_prot(): idx = type + KM_TYPE_NR*smp_processor_id();