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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id g3sm11218876edk.75.2021.02.15.10.12.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Feb 2021 10:12:53 -0800 (PST) From: Vitaly Kuznetsov To: Igor Mammedov Subject: Re: [PATCH v4 16/21] i386: track explicit 'hv-*' features enablement/disablement In-Reply-To: <20210215165502.64e1e629@redhat.com> References: <20210210164033.607612-1-vkuznets@redhat.com> <20210210164033.607612-17-vkuznets@redhat.com> <20210211183555.2136b5c8@redhat.com> <87tuqhllmn.fsf@vitty.brq.redhat.com> <20210212151259.3db7406f@redhat.com> <87k0rdl3er.fsf@vitty.brq.redhat.com> <87h7mhl33o.fsf@vitty.brq.redhat.com> <20210212170527.0e93e6b2@redhat.com> <87blcllnf0.fsf@vitty.brq.redhat.com> <20210215165502.64e1e629@redhat.com> Date: Mon, 15 Feb 2021 19:12:52 +0100 Message-ID: <87pn11jj2z.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vkuznets@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: Paolo Bonzini , drjones@redhat.com, Marcelo Tosatti , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Igor Mammedov writes: > On Mon, 15 Feb 2021 09:56:19 +0100 > Vitaly Kuznetsov wrote: > >> Igor Mammedov writes: >> >> > On Fri, 12 Feb 2021 16:26:03 +0100 >> > Vitaly Kuznetsov wrote: >> > >> >> Vitaly Kuznetsov writes: >> >> >> >> > Igor Mammedov writes: >> >> > >> >> >> >> >> >> Please try reusing scratch CPU approach, see >> >> >> kvm_arm_get_host_cpu_features() >> >> >> for an example. You will very likely end up with simpler series, >> >> >> compared to reinventing wheel. >> >> > >> >> > Even if I do that (and I serioulsy doubt it's going to be easier than >> >> > just adding two 'u64's, kvm_arm_get_host_cpu_features() alone is 200 >> >> > lines long) this is not going to give us what we need to distinguish >> >> > between >> >> > >> >> > 'hv-passthrough,hv-evmcs' >> >> > >> >> > and >> >> > >> >> > 'hv-passthrough' >> >> > >> >> > when 'hv-evmcs' *is* supported by the host. When guest CPU lacks VMX we >> >> > don't want to enable it unless it was requested explicitly (former but >> >> > not the later). >> >> >> >> ... and if for whatever reason we decide that this is also bad/not >> >> needed, I can just drop patches 16-18 from the series (leaving >> >> 'hv-passthrough,hv-feature=off' problem to better times). >> > that's also an option, >> > we would need to make sure that hv-passthrough is mutually exclusive >> > with ''all'' other hv- properties to avoid above combination being >> > ever (mis)used. >> >> That's an option to finally get these patches merged, not a good option >> for end users. >> >> 'hv-passthrough,hv-feature' works today and it's useful. Should we drop >> it? > well, > try suggested idea about using scratch CPU and it might get merged sooner. > (it's not like I'm suggesting you to rewrite half of QEMU, just some of > patches, which most likely would simplify series from my point of view > and would be easier to maintain) > I don't see anything in the series which will go away if I implement this idea but as I hate it deerly I'm likely not going to. -- Vitaly