From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pg0-x233.google.com ([2607:f8b0:400e:c05::233]) by Galois.linutronix.de with esmtps (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1fJio2-0005c5-TJ for speck@linutronix.de; Fri, 18 May 2018 19:04:39 +0200 Received: by mail-pg0-x233.google.com with SMTP id e1-v6so3575873pga.6 for ; Fri, 18 May 2018 10:04:38 -0700 (PDT) Received: from i7.lan (c-73-11-52-149.hsd1.or.comcast.net. [73.11.52.149]) by smtp.gmail.com with ESMTPSA id g26-v6sm16440887pfh.76.2018.05.18.10.04.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 18 May 2018 10:04:31 -0700 (PDT) Sender: Linus Torvalds Date: Fri, 18 May 2018 10:04:29 -0700 (PDT) From: Linus Torvalds Subject: [MODERATED] Re: AMD SSBD extension document In-Reply-To: <20180518164002.gp72oy264fmtjb6t@ast-mbp.dhcp.thefacebook.com> Message-ID: References: <20180518164002.gp72oy264fmtjb6t@ast-mbp.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit To: speck@linutronix.de List-ID: On Fri, 18 May 2018, speck for Alexei Starovoitov wrote: > > Like, does it disable store-to-load forwarding out of store queue as well? It really shouldn't, and based on the (limited) performance data I've seen I don't think it does. Afaik it only disabled the speculative case of reading the data early when a previous store hasn't even entered the store buffer yet because the store address isn't known. So it's actually the exact reverse of your worry - the bug is that CPU's will *not* snoop the store buffer (or snoop an even earlier wrong entry in the store buffer), because they'll try to do the read speculatively early. Linus