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Mon, 04 Nov 2024 06:52:50 -0800 (PST) Received: from [10.125.226.166] ([185.25.67.249]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5cec86a4ef2sm2765279a12.3.2024.11.04.06.52.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Nov 2024 06:52:49 -0800 (PST) Message-ID: Date: Mon, 4 Nov 2024 14:52:48 +0000 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: amit.shah@amd.com Cc: Babu.Moger@amd.com, David.Kaplan@amd.com, Sandipan.Das@amd.com, Thomas.Lendacky@amd.com, boris.ostrovsky@oracle.com, bp@alien8.de, corbet@lwn.net, daniel.sneddon@linux.intel.com, dave.hansen@linux.intel.com, hpa@zytor.com, jpoimboe@kernel.org, kai.huang@intel.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, pawan.kumar.gupta@linux.intel.com, pbonzini@redhat.com, peterz@infradead.org, seanjc@google.com, tglx@linutronix.de, x86@kernel.org References: Subject: Re: [PATCH 1/2] x86: cpu/bugs: add support for AMD ERAPS feature Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit > Unfortunately, that's all we have right now in the official > documentation. > > I've put up some notes in > https://amitshah.net/2024/11/eraps-reduces-software-tax-for-hardware-bugs/ I appreciate the attempt to get a few details out, but this is very confused on bunch of details. Most importantly, you've described Intel RSB underflows, but named it AMD BTC. "Retbleed" is two totally different things.   I begged the discoverers to give it two names, and I also begged the x86 maintainers to not alias them in Linux's view of the world, but alas. AMD's BTC comes from a bad branch type prediction, and a late resteer from the ret uop executing.   It has nothing to do with RAS/RSB underflow conditions. ~Andrew