From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38239) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fT9NW-0005qX-Hs for qemu-devel@nongnu.org; Wed, 13 Jun 2018 13:16:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fT9NT-0007Bw-3X for qemu-devel@nongnu.org; Wed, 13 Jun 2018 13:16:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56092) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fT9NS-0007A7-Sp for qemu-devel@nongnu.org; Wed, 13 Jun 2018 13:16:11 -0400 Date: Wed, 13 Jun 2018 14:16:07 -0300 From: Eduardo Habkost Message-ID: <20180613171607.GB7451@localhost.localdomain> References: <20180611203712.12086-1-ehabkost@redhat.com> <20180612150153.GK7451@localhost.localdomain> <6c9b3744-7323-cd1f-7b07-2b77df7ae80d@redhat.com> <20180612182541.GN7451@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [RFC PATCH] i386: Remove ospke CPUID flag name List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: qemu-devel@nongnu.org, Richard Henderson On Wed, Jun 13, 2018 at 07:01:23PM +0200, Paolo Bonzini wrote: > On 12/06/2018 20:25, Eduardo Habkost wrote: > > On Tue, Jun 12, 2018 at 05:12:58PM +0200, Paolo Bonzini wrote: > >> On 12/06/2018 17:01, Eduardo Habkost wrote: > >>>>> > >>>>> Remove OSPKE from the feature name array so users don't try to > >>>>> configure it manually. > >>>>> > >>>>> Signed-off-by: Eduardo Habkost > >>>> Yes, it's the same as OSXSAVE. Thanks! > >>> CR4_OSXSAVE_MASK is automatically enabled on user-mode QEMU, > >>> though. > >>> > >>> My question is if it would make any sense to enable CR4_PKE_MASK > >>> too. > >> > >> If you mean OSPKE, then yes---if PKU is available. Likewise, OSXSAVE > >> should only be enabled if XSAVE is available. > > > > Yeah, I mean enabling it only if PKU is available, like we > > already do with OSXAVE/XSAVE. > > > > But we don't do it today, so enabling it automatically in > > CONFIG_USER_ONLY would be a new feature. Would it be useful for > > anything, though? > > > > I'm asking that to find out if somebody could be already using > > "-cpu ...,+ospke" with user-mode QEMU today (which this patch > > would break). If RDPKRU/WRPKRU is useless under user-mode QEMU, > > than we don't need to worry about that. > > Hmm, actually there are two more things to consider for user-mode emulation. > > First, QEMU doesn't support any of pkey_mprotect, pkey_alloc, pkey_free, > so it should probably never set OSPKE. This means "-cpu ...,+ospke" is useless today and we can safely remove support for it, right? > Second, for user-mode emulation it makes sense to allow flipping of > OSPKE and OSXSAVE, because that corresponds to different behaviors of > the underlying kernels. There have been bugs in fact with programs that > incorrectly tested XSAVE instead of OSXSAVE, so it's worthwhile to let > the user test both configurations. However, "-cpu ...,-osxsave" has no effect today (user-mode QEMU unconditionally sets OSXSAVE), so that would be a new feature. I assume this means I don't need to drop the osxsave patch from my queue, either. > So to sum up, the default for QEMU user-mode emulation should be > OSXSAVE=XSAVE and OSPKE=0. Thanks! -- Eduardo