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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C4EDCC10F1A for ; Tue, 7 May 2024 14:24:25 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.718212.1120773 (Exim 4.92) (envelope-from ) id 1s4Lju-00062Z-IM; Tue, 07 May 2024 14:24:18 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 718212.1120773; Tue, 07 May 2024 14:24:18 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1s4Lju-00062S-Fh; Tue, 07 May 2024 14:24:18 +0000 Received: by outflank-mailman (input) for mailman id 718212; Tue, 07 May 2024 14:24:17 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1s4Ljt-00061o-68 for xen-devel@lists.xenproject.org; Tue, 07 May 2024 14:24:17 +0000 Received: from mail-oi1-x235.google.com (mail-oi1-x235.google.com [2607:f8b0:4864:20::235]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 7acf9374-0c7d-11ef-b4bb-af5377834399; Tue, 07 May 2024 16:24:15 +0200 (CEST) Received: by mail-oi1-x235.google.com with SMTP id 5614622812f47-3c86f066256so1799189b6e.2 for ; Tue, 07 May 2024 07:24:15 -0700 (PDT) Received: from localhost ([213.195.114.223]) by smtp.gmail.com with ESMTPSA id r9-20020a0cf809000000b006a0ecb2333esm4735874qvn.99.2024.05.07.07.24.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 May 2024 07:24:13 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 7acf9374-0c7d-11ef-b4bb-af5377834399 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1715091854; x=1715696654; darn=lists.xenproject.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=+HzMSaFTxW/BpNWP9DdNLYLF5hdPWgxP7OVUISaXBrU=; b=WvSCr0/7ECf+wpT3bR/xmPXb4K30C4pceJnMydLESpmoOgvW3a02j5YcogBmIO/kMy k4aUGotmFj+Weugygg8mXbzr7B/iLn130LX8imyIUYmca86v60i5urZRp+C94AWBbJMl 83yE7AhqMcoYxofVinmPxMP5cbwnd8FpudSnk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1715091854; x=1715696654; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=+HzMSaFTxW/BpNWP9DdNLYLF5hdPWgxP7OVUISaXBrU=; b=pn2I2Cbk1JYjOZJoOK6weRhJUjdYihEwOPk395BRRUkn0tH4vpZw2H2Jn+I1tH8Kak pX1b83pPdZMhQNkXOS4tnaz8ttndh+G7bx4pIp3IQtD9suiR8DN7Pm32HqT82I4Q35ED +YfUI5HTjGas4Y4XUc+yvL9B2cl/mSaMSRNjVGNhDUZad0SE0Yz7E0PRYME5YxAu7gU/ 2V4BGGsw8icOuOtfXAviria+/RYT6zFk3uGG7wj9nm/Tqg+wjiK5uOuYgbKAM4LALCB2 cd6sgm1fcom9kmkDdKvuR2zBcP+qGYXDEriJnpmh5+frPwgS1W1HW8AtMsKs34pjIO7t 6Dfg== X-Gm-Message-State: AOJu0Yx3R3PmpzerxeuL4XQIVR/VyS5REai5pUFpmQxJlxy9hPh4kir4 hEUYLryFpXZVGHlIUs4qHclNBdsavX7WL9sss+GzG4zanDbhvxDrdEadgZkoPjQ= X-Google-Smtp-Source: AGHT+IHdu0GbLBLq8xrWB7P1x0kX0CqfibMyyb+mstpbF5UTNoLMg64Yh3Dd9ZTvP4qbCrEBQNRZCA== X-Received: by 2002:aca:90a:0:b0:3c9:7003:af7e with SMTP id 10-20020aca090a000000b003c97003af7emr5226265oij.18.1715091853672; Tue, 07 May 2024 07:24:13 -0700 (PDT) Date: Tue, 7 May 2024 16:24:11 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Andrew Cooper Cc: Xen-devel , Jan Beulich Subject: Re: [PATCH v2] x86/cpu-policy: Fix migration from Ice Lake to Cascade Lake Message-ID: References: <20240507112957.1701824-1-andrew.cooper3@citrix.com> <20240507134540.1714274-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240507134540.1714274-1-andrew.cooper3@citrix.com> On Tue, May 07, 2024 at 02:45:40PM +0100, Andrew Cooper wrote: > Ever since Xen 4.14, there has been a latent bug with migration. > > While some toolstacks can level the features properly, they don't shink > feat.max_subleaf when all features have been dropped. This is because > we *still* have not completed the toolstack side work for full CPU Policy > objects. > > As a consequence, even when properly feature levelled, VMs can't migrate > "backwards" across hardware which reduces feat.max_subleaf. One such example > is Ice Lake (max_subleaf=2 for INTEL_PSFD) to Cascade Lake (max_subleaf=0). > > Extend the max policies feat.max_subleaf to the hightest number Xen knows > about, but leave the default policies matching the host. This will allow VMs > with a higher feat.max_subleaf than strictly necessary to migrate in. > > Eventually we'll manage to teach the toolstack how to avoid creating such VMs > in the first place, but there's still more work to do there. > > Signed-off-by: Andrew Cooper Acked-by: Roger Pau Monné Even if we have just found one glitch with PSFD and Ice Lake vs Cascade Lack, wouldn't it be safer to always extend the max policies max leafs and subleafs to match the known array sizes? Thanks, Roger.