From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225hutnizkQmMD9l80JfgnYfHaDv8r/OulGnu1/ndBzub5pSPoG73hRN1cozYXxd31o4O4Pj ARC-Seal: i=1; a=rsa-sha256; t=1517313855; cv=none; d=google.com; s=arc-20160816; b=PZ/iqOyOWfNNxQVPECK8GkeakIFxvzQH/gSMimzu7rh2YD4q+AqZayeBr64BPuoz+g vQVh8UtDxuPzrXszgfOjlixRFIxtpvvP2qg//Nve75L/1PnvJRPenr/abKdoTR6I9ngX EZexIR77O+kUdZOKxqG2wNfbZfOYH/u8OB7ovVmirRbr7S1EXRbFG0WttTxXKwdCRI+J O8xipY8L1QVvJEce6hWn0ItdZ4wS8hA0pnLkpOalCV5Tj/hzr+HP4SBmUfntWtiFc1aF a5ztimgF7Mf97560CxrZ+AFPXclxsY71+Nc+Eim5ofocwL/3e2fC3ZwTfJyUJnVOQxIb DJxw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:arc-authentication-results; bh=4H7umlLvTetdjWynGKUDk3YReQ4d6UG5UllF2Y8WGg8=; b=OapHXRFcWUXd4F/DNNOOnukf1Ah3NcjQNJkOxRPHXwWh2XlK3vI79P06aF8FzkNCjL 3nuCV4c5+Nr7SvnVPLx0CSlKB32NKzGVkHoG5gWnwSwA1mOVLdubGGiK6X2BGJbHq/ZH 36G2yUahjQ8+kOGkx4cCBaU6Wwr3tsqOOlxEe54EIneDzonsFcAKHFr3VtSQg48GQf0g mOzIBdxnmEPuxCbIyDLCHdnhIPIB5chROCxKWe/d2410hsXFdSjVlAFWZCwny2PL5tPc Ez18v23K4v8ncn+z9FsedR0gEKznPIypa2iksrz1uSoSUdvxZp0Rba6xXygAeCTdcSSs 5XGA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Date: Tue, 30 Jan 2018 10:04:09 -0200 From: Eduardo Habkost To: Linus Torvalds Cc: Arjan van de Ven , David Woodhouse , KarimAllah Ahmed , Linux Kernel Mailing List , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , Tom Lendacky , KVM list , the arch/x86 maintainers , "Dr. David Alan Gilbert" Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure Message-ID: <20180130120409.GA26425@localhost.localdomain> References: <1516476182-5153-6-git-send-email-karahmed@amazon.de> <20180129201404.GA1588@localhost.localdomain> <1517257022.18619.30.camel@infradead.org> <20180129204256.GV25150@localhost.localdomain> <31415b7f-9c76-c102-86cd-6bf4e23e3aee@linux.intel.com> <1517259759.18619.38.camel@infradead.org> <6c024f95-b12c-9c66-91d7-208ed2c380ff@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Fnord: you can see the fnord User-Agent: Mutt/1.9.1 (2017-09-22) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140581449802182?= X-GMAIL-MSGID: =?utf-8?q?1591018892824379455?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Mon, Jan 29, 2018 at 07:32:06PM -0800, Linus Torvalds wrote: > On Mon, Jan 29, 2018 at 5:32 PM, Arjan van de Ven wrote: > > > > the most simple solution is that we set the internal feature bit in Linux > > to turn on the "stuff the RSB" workaround is we're on a SKL *or* as a guest > > in a VM. > > That sounds reasonable. > > However, wouldn't it be even better to extend on the current cpuid > model, and actually have some real architectural bits in there. If Intel could do that, it would be great. > > Maybe it could be a bit in that IA32_ARCH_CAPABILITIES MSR. Say, add a > bit #2 that says "ret falls back on BTB". > > Then that bit basically becomes the "Skylake bit". Hmm? Yes. But note that the OS needs to be able to differentiate "old Skylake that doesn't support the new bit" from "newer Skylake that doesn't fall back om BTB". That's why I suggest a "non-Skylake bit" instead of a "Skylake bit". -- Eduardo