From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D29F7EE49A3 for ; Wed, 23 Aug 2023 05:20:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232671AbjHWFUD (ORCPT ); Wed, 23 Aug 2023 01:20:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232660AbjHWFT7 (ORCPT ); Wed, 23 Aug 2023 01:19:59 -0400 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 87FC5E54 for ; Tue, 22 Aug 2023 22:19:57 -0700 (PDT) Received: from nazgul.tnic (unknown [78.130.214.203]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 07D811EC04CC; Wed, 23 Aug 2023 07:19:55 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1692767996; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=75aTNDR6HJinTwoq5er6R7fMgm56ytnfyZ2eCO+tpcU=; b=UcZZeZKm4iK1L3vtdhgw8HFILczt1bRi/e8z5mPVoJthlxUGFPKB13aZCATkqzdE5HktfW 987jN87lrWYKpdNLHKxKUx/rrgwHhjEN8HVqSBJObf3sEMHYSs0RXxmp9ia54g1dkC4ggv KMN8GOPUofLbIkxUOCBC53LeCysIU6E= Date: Wed, 23 Aug 2023 07:20:07 +0200 From: Borislav Petkov To: Andrew Cooper Cc: Josh Poimboeuf , x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Babu Moger , Paolo Bonzini , Sean Christopherson , David.Kaplan@amd.com, Nikolay Borisov , gregkh@linuxfoundation.org, Thomas Gleixner Subject: Re: [PATCH 02/22] x86/srso: Set CPUID feature bits independently of bug or mitigation status Message-ID: <20230823052007.GBZOWXBymcCUOoMax3@fat_crate.local> References: <26a3421e-3a88-b326-4c4f-abdaa2262852@citrix.com> <20230821140619.GBZONvWz+iwQZwx/sC@fat_crate.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230821140619.GBZONvWz+iwQZwx/sC@fat_crate.local> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 21, 2023 at 04:06:19PM +0200, Borislav Petkov wrote: > And I still don't know what exactly we're going to support when Linux > runs as a guest. For example, live migration between Zen1/2 and Zen3/4 > won't work due to the alternatives patching, for example... > > IBPB won't work either because we detect those feature bits only once > during boot, like every other feature bit... The lowest common denominator of features exposed to the guests, should work, as I'm being told. As in, Zen2 and Zen3 should hide the SBPB bit from the guests, for example. Anything else like kernel code patching based on early detection of features won't fly. But that has never flown anyway unless you don't change that set of features. I'm thinking if anyone cares really deeply about live migration, anyone should say so and then we can see what cases we can support upstream. My guess is those who do, have enough engineers to patch their kernel the way they want it... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette