Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v3] Documentation: Add section about CPU vulnerabilities
 for Spectre
From:   Jon Masters <jcm@redhat.com>
To:     Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ben Greear <greearb@candelatech.com>, stable@vger.kernel.org,
        Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Jiri Kosina <jikos@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Waiman Long <longman9394@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Mark Gross <mgross@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org
References: <c63945d34bfc9df2412f813d0b9b3a321a65de5d.1560795378.git.tim.c.chen@linux.intel.com>
 <5ff842bb-e0b8-c4aa-134d-32c9d838a162@redhat.com>
Openpgp: preference=signencrypt
Autocrypt: addr=jcm@redhat.com; keydata=
 mQINBE6Ll1oBEADNCMsChhQGT2JDjJPzACWwz2LgW9Scrzg7fMuB0QCZUWwYiFn8aSnWbF1D
 gW8zLaylIUBcoSZNNPQ3S03pHmFtCwCPESaCI/TikHlGA6c996jZzf1zLx/khEecBC1b4pFM
 VbWzE0RosgXotxu0MCaAp3mLOFWRZJu4BHGuSSuqbT4qfJ1euIN4uSD7+GG5M/O3ERIoYV3Q
 E8FBUUKKDRXdI8e1fq7iqg59Dq4P922iuhpbdwQRTRQmb+4uuRaJG7PMP5uBtN+Y0umvYK/y
 ha1kFqunGQ95GTSleD3E5ifjXWAOLjOldl4fxw6a5Z2fbX+uTancr8G85JLzhQp4+0Av5WfV
 MGe+UCUH8nlfJDzFE0q/oltgXDwE+4Pr9J8NSN4heF8XL5Cn6JnE9d/YvgIGEmyf6J/8WPQ+
 nWTqN+VvEkrvn5oHuJOuM16AFRptUFQOJQGCIK/hupwHkR6TjFMA2XLv6CXjAgvWK+z9SAw8
 zUFcqDN983qD3pc88lmSgPp7uArmMwBdCEpVayCLvu+M5kzZz9rty73u3Rv1MF0o+Rtdq4uc
 JLhjCd/FAMTXi5VzkBcuOufgcvqs0kFgloCvdL72+dyowYDJaC8Ir6KNrz3iOk9P56ESY8E3
 70/wkoyfVnesrih7ntiqltISotRR7lDp4AD8oskaAcGqKy3AYQARAQABtDdKb24gTWFzdGVy
 cyAoSm9uYXRoYW4gQ2hhcmxlcyBNYXN0ZXJzKSA8amNtQHJlZGhhdC5jb20+iQI4BBMBAgAi
 BQJOi5fqAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDkIJuMiuip0RN0D/9Ck2/i
 xD+1F5iYvXwkSSlZzaoWuQiidaRdF4x4QD4QmPpva5CB1GpUcIjwyW9gBYLVMSJq8tcb1FnX
 Hce/pP/0K+p+wI9sH/xK4jQ+CkIHdw8o1i7EWKznxP3gEN5B5k2Qfh0XHoLjNyXQHZc47aFS
 I6W6m0iVpS1HNW22gk3TpN9GfOpiUA/BRmjsIPRdAd3kZAEmhCNwL0W5qfJPahIgYlcCk4R0
 Azw6bjvox87+bf3h36QLENcXKpA5Mv09gIsnNoa+bfHtoTkXW2le+/vM0VGEnMUUuUKGmxjY
 H9LyRyDEvq1XD9aF9WsHyRn7Kip2MrtwRdGpLobe8OIxYw2vkojfDI6cM/HwLeqNn1wBLkfq
 J8ZtOyGGlkTaNqLVDopNS4jJlMe59Ir345N4UaTrN5hJq0Utn/jsej1v8y5kH4ZRFasodTd+
 IytUO0k8lSod6xPF7lM3QmmXjhJFzmnLtyxeKH7csboejLX97b7Y93y3nNOTQJulb01mcLBY
 6nW49fOAOVbTk4BdmIRMlhR/eX/dWEWLWV0RpQk1IgIFQULLBI5xLazCz41I1EyK0nmxnarw
 5n4S5tBLxGdl/z8mmkPQkQklwEiEGgb773VTQQxHB3/4DTBHVZ5iYX3mt0Bm3Vm2GyJyMtPb
 Dl5TijAxP5i39cOizPIcoiU6PLdisLkCDQROi5daARAAuB7uqbo8oWZlkniNFb/AkTruoUp6
 ak+VKLrueaQ5HPVVx4maEUdTsk9mZRlBB6nPXQJAHW/jI0qBqG7hFmhZdRN9Ag2bjGbtuK44
 zg/9/dt86n8ASKqu8Q9z1MAslPwm++S9rE02Oif5mlfIl62zlUZhi+ChvaCM+NbZ7u17edo2
 0QHnFIQwBqlA29xFzjq9pnzpIe0xxLLuuG8yFe/yWfwAnI1S9Yp5UlDdmF6GMtRroXtmxPud
 SnMk6K5wvtvY2mkBSc96ug4EYyZfFyUxjnAfcANFCRGnTyF6XxPOBzhKMeYDBu/SIHCyhF2V
 QFLdSYa0uGSdjqf0hgd09TDa/r7b/pytxJP8+6AZXgQ93JlB+rYfvaLcjypgmPhxXX8UugH8
 GaeZGaFZcYvkdsmjE6SWZuM0QfsML9BdSvFT6+Bf0c45rEhO2c8NTyFUsdqC51C1vamReR6R
 hTc7TFclT++/n29N0ns70edn2lMQ/lDN3uNkQV2xABXFrT1yXdkwN1/7dGnv/4Q+4ihrXJcr
 y6CP6DJJuIiIRK/x6AVszd4S/2PjmxLiSLpuPLjQ18ZsUJrzqDO7Cc46QTgizVTu+sTEL195
 J6quiELm3MB9Ut+6EKzSoJUdNnF/PE/HkzTssQlxZWdO8Yyw3GF2HtHfcyZrW6ZDrZEsnhUC
 otkmigsAEQEAAYkCHwQYAQIACQUCTouXWgIbDAAKCRDkIJuMiuip0eDBD/9rj2V4zO+DWtY0
 HCIn5Cz7HBSw8hRs8orv1QQYUoDZBn5zqIdmjc1SCyNOqTXEEBAnruPE9vxgI0QkuW9uyAWh
 wL7+rzHZefUx5H2HI1FPGfPL5we37gnpf1S+PhOKobd3KKaiQ0DFqdTqPlZIkGXChIXPF0bG
 g6HSY/vVHYC4Rqysj/Sw+74nGzJRSisNt60W0LPRcWdbEX4zEvdUJX4YAbUBoEKLOt1VmRXt
 UeC8hgVOuIxkIVsWlHgVlztn0e0BtOutlR5Lu28D/CWObjHJG6+Kq0PgUiFiHmUFpAhiuPyO
 nwZOLHdVxflxJBdO8GVRV6GqygZQ8fcg/neDb2waYRBUOROEMzNn5+tG11QBbbYLoBL8eKt3
 kgaSfasOaWV5e1+Y6OkZXfjlYqbLkgaFB7ZizUlfsq9sp/aAlAfU5hUISSCaSMinRUQTy6+y
 +9WGZrrwsWZO7wdq1ccGE6bXFRWhteq5UIJS8cg0m0vnrsv9GddFBeNaF34Ye9hlD05ofBuc
 PTfbCfHxsndrq+vPPR64uZrh9i7qO/KFZwKns4yGhO78umvHuyinOvEHA2Of1bOP/ohIbTAz
 VHjokMI4EXkVzgVP9EgwzBwX1PWi6OEFIG0yWltbmFXnn3clTIa/uG1c0VpCRuGtSEtqfC7n
 yrXvw9qg2waGcnb8WuoS+g==
Message-ID: <526833c7-b9b4-1847-9f9b-52dd248548ad@redhat.com>
Date:   Mon, 17 Jun 2019 16:30:26 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.4.0
MIME-Version: 1.0
In-Reply-To: <5ff842bb-e0b8-c4aa-134d-32c9d838a162@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 6/17/19 4:22 PM, Jon Masters wrote:

>> +   For kernel code that has been identified where data pointers could
>> +   potentially be influenced for Spectre attacks, new "nospec" accessor
>> +   macros are used to prevent speculative loading of data.
> 
> Maybe explain that nospec (speculative clamping) relies on the absence
> of value prediction in the masking (in current hardware). It may NOT
> always be a safe approach in future hardware, where Spectre-v1 attacks
> are likely to persist but hardware may speculate about the mask value.

Something like the Arm CSDB barrier would seem to be potentially useful
for $FUTURE_X86 as a fence with lighter-weight semantics than an *fence.

Jon.

-- 
Computer Architect | Sent with my Fedora powered laptop