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[2001:8b0:bb71:7140:64::1]) by smtp.gmail.com with ESMTPSA id h9sm2965025wme.11.2021.01.20.02.08.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Jan 2021 02:08:12 -0800 (PST) Received: from localhost (disaster-area.hh.sledj.net [local]) by disaster-area.hh.sledj.net (OpenSMTPD) with ESMTPA id 564a8a90; Wed, 20 Jan 2021 10:08:11 +0000 (UTC) To: Igor Mammedov , Eduardo Habkost Subject: Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature In-Reply-To: <20210120105924.3ffd1723@redhat.com> References: <20210119142207.3443123-1-david.edmondson@oracle.com> <20210119142207.3443123-2-david.edmondson@oracle.com> <20210119152056.GE1227584@habkost.net> <20210119163052.GG1227584@habkost.net> <20210120105924.3ffd1723@redhat.com> X-HGTTG: zarquon From: David Edmondson X-Now-Playing: Four Tet - Sixteen Oceans: Insect Near Piha Beach Date: Wed, 20 Jan 2021 10:08:11 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Received-SPF: neutral client-ip=2a00:1450:4864:20::329; envelope-from=dme@dme.org; helo=mail-wm1-x329.google.com X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NEUTRAL=0.779, UNPARSEABLE_RELAY=0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wednesday, 2021-01-20 at 10:59:24 +01, Igor Mammedov wrote: > On Tue, 19 Jan 2021 11:30:52 -0500 > Eduardo Habkost wrote: > >> On Tue, Jan 19, 2021 at 04:27:56PM +0000, David Edmondson wrote: >> > On Tuesday, 2021-01-19 at 10:20:56 -05, Eduardo Habkost wrote: >> > >> > > Hi, >> > > >> > > Thanks for the patch. Getting rid of special -feature/+feature >> > > behavior was in our TODO list for a long time. >> > > >> > > On Tue, Jan 19, 2021 at 02:22:06PM +0000, David Edmondson wrote: >> > >> "Minus" features are applied after "plus" features, so ensure that a >> > >> later "plus" feature causes an earlier "minus" feature to be removed. >> > >> >> > >> This has no effect on the existing "-feature,feature=on" backward >> > >> compatibility code (which warns and turns the feature off). >> > > >> > > If we are changing behavior, why not change behavior of >> > > "-feature,feature=on" at the same time? This would allow us to >> > > get rid of plus_features/minus_features completely and just make >> > > +feature/-feature synonyms to feature=on/feature=off. >> > >> > Okay, I'll do that. >> > >> > Given that there have been warnings associated with >> > "-feature,feature=on" for a while, changing that behaviour seems >> > acceptable. >> > >> > Would the same be true for changing "-feature,+feature"? (i.e. what this >> > patch does) Really: can this just be changed, or does there have to be >> > some period where the behaviour stays the same with a warning? >> >> I actually expected warnings to be triggered when using >> "-feature,+feature" as well. If we were not generating warnings >> for that case, it will need more careful evaluation, just to be >> sure it's safe. Igor, do you remember the details here? > As part of preparation to define/create machines via QMP, > I plan to post patch(s) to deprecate +-features in 6.0 > (including special casing for -feat behavior (affects x86/sparc only)) > and drop support for +-feat in 2 releases. > So we should end up with canonical property behavior only like all other > CPUs and devices. In that case I will abandon this change and focus on getting my upstack consumer to switch away from using +-. Thanks. dme. -- Sometimes these eyes, forget the face they're peering from.