From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx.treblig.org (mx.treblig.org [46.235.229.95]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D3F892BF01B for ; Mon, 16 Jun 2025 23:33:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=46.235.229.95 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750116822; cv=none; b=TdF4lnEN1mYzSkFTn1b4PkzakcHj58HH6CpYbN76CQ95tFZVK6tS38oyp5wNch+WpFVkYQTb5n0K/LqnCUXDKLJ8ioF2cl5LjIHzT74GDYC/ZD8IU/Bp/5B+VUi1nxfG8dTIn2SDVs/dzCP7vGDCvdVbrP2Uy0iaT/Z7/Or/gWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750116822; c=relaxed/simple; bh=r9V7Lv9bIf/ES5N/fxOfdN1RijU6kclvrc1CLeiQvxM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=sIhTFDmVQg7UAEnPMr/c+Go+ClSaj45s6pyRqZFFehoCs+epHxG9RZsi5WmYS4QKFwIrXbuJ0G/3vi8aq6ypx5wywzvo0xua+qCWxZomHwQWQrOmaxCHLcZ5yyzktN5C/cpG6MEH4lsKL9lmZrYlF8K2h549I2DAaqUGpmDbNEY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=treblig.org; spf=pass smtp.mailfrom=treblig.org; dkim=pass (2048-bit key) header.d=treblig.org header.i=@treblig.org header.b=El/fY8UI; arc=none smtp.client-ip=46.235.229.95 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=treblig.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=treblig.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=treblig.org header.i=@treblig.org header.b="El/fY8UI" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=treblig.org ; s=bytemarkmx; h=Content-Type:MIME-Version:Message-ID:Subject:From:Date:From :Subject; bh=FQ9AVie1G3opC6SktC6DwSQCFYiO015Exy38SxOe1kk=; b=El/fY8UIGmwy+hKD EFhjQDl6etqkbrwFleIO3W6yF4k4S3PZaDqzEGa53I6uVPjWSrA2OMlrnk29YkRiUrNi5Fv76onDf g3hkgz9OhChZS8KQ4s7LqiwkmLLP54gyWaymsal1W0yypK8KBWOZms7pY8LHapFvYT4fG+q2mRMwk odt08sf/0Ld6EXU3ftcHABuXhS51hlEDB+OjXpUtX+pdCiwKSXfK5IHBzyAhKj39W42jChEG/SpfA wlt2AFahovgmX0NYmA+3vlj9OUg5uEiK+Y9JsI0lqQNaQvQZc8/BfUkw9fE+hlboBNxrFIePOImfH pgA0S/LMuz7lF5pinw==; Received: from dg by mx.treblig.org with local (Exim 4.96) (envelope-from ) id 1uRJKO-009ze4-2z; Mon, 16 Jun 2025 23:33:24 +0000 Date: Mon, 16 Jun 2025 23:33:24 +0000 From: "Dr. David Alan Gilbert" To: "Moger, Babu" Cc: pbonzini@redhat.com, zhao1.liu@intel.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, davydov-max@yandex-team.ru Subject: Re: [PATCH v7 4/6] target/i386: Add couple of feature bits in CPUID_Fn80000021_EAX Message-ID: References: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Chocolate: 70 percent or better cocoa solids preferably X-Operating-System: Linux/6.1.0-34-amd64 (x86_64) X-Uptime: 23:28:48 up 50 days, 7:42, 1 user, load average: 0.00, 0.00, 0.00 User-Agent: Mutt/2.2.12 (2023-09-09) * Moger, Babu (babu.moger@amd.com) wrote: > Hi Dave, > > On 6/6/25 07:29, Dr. David Alan Gilbert wrote: > > * Babu Moger (babu.moger@amd.com) wrote: > >> Add CPUID bit indicates that a WRMSR to MSR_FS_BASE, MSR_GS_BASE, or > >> MSR_KERNEL_GS_BASE is non-serializing amd PREFETCHI that the indicates > >> support for IC prefetch. > >> > >> CPUID_Fn80000021_EAX > >> Bit Feature description > >> 20 Indicates support for IC prefetch. > >> 1 FsGsKernelGsBaseNonSerializing. > > > > I'm curious about this: > > a) Is this new CPUs are non-serialising on that write? > > b) If so, what happens if you run existing kernels/firmware on them? > > c) Bonus migration question; what happens if you live migrate from a host > > that claims to be serialising to one that has the extra non-serialising > > flag but is disabled in the emulated CPU model. > > Good question. After looking at the AMD64 Architecture Programmer’s Manual > again, these writes have always been non-serializing. Behavior has not > changed. Ah OK, then nothing to worry about. > We're just reporting it through CPUID now. This information > likely isn’t being used anywhere. Seems curious to add it then! > Let me know if you have any questions. No, thanks for the reply. Dave > -- > Thanks > Babu Moger -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/