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Tue, 31 Jan 2023 14:00:45 +0000 Date: Tue, 31 Jan 2023 14:00:44 +0000 Message-ID: <86cz6u248j.wl-maz@kernel.org> From: Marc Zyngier To: Suzuki K Poulose Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Alexandru Elisei , Andre Przywara , Chase Conklin , Christoffer Dall , Ganapatrao Kulkarni , Jintack Lim , Russell King , James Morse , Oliver Upton , Zenghui Yu Subject: Re: [PATCH v8 01/69] arm64: Add ARM64_HAS_NESTED_VIRT cpufeature In-Reply-To: References: <20230131092504.2880505-1-maz@kernel.org> <20230131092504.2880505-2-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: suzuki.poulose@arm.com, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, alexandru.elisei@arm.com, andre.przywara@arm.com, chase.conklin@arm.com, christoffer.dall@arm.com, gankulkarni@os.amperecomputing.com, jintack@cs.columbia.edu, rmk+kernel@armlinux.org.uk, james.morse@arm.com, oliver.upton@linux.dev, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230131_060048_461223_CED2E076 X-CRM114-Status: GOOD ( 22.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Suzuki, On Tue, 31 Jan 2023 13:47:31 +0000, Suzuki K Poulose wrote: > > Hi Marc > > On 31/01/2023 09:23, Marc Zyngier wrote: > > From: Jintack Lim > > > > Add a new ARM64_HAS_NESTED_VIRT feature to indicate that the > > CPU has the ARMv8.3 nested virtualization capability, together > > with the 'kvm-arm.mode=nested' command line option. > > > > This will be used to support nested virtualization in KVM. > > > > Reviewed-by: Russell King (Oracle) > > Signed-off-by: Jintack Lim > > Signed-off-by: Andre Przywara > > Signed-off-by: Christoffer Dall > > [maz: moved the command-line option to kvm-arm.mode] > > Should this be separate kvm-arm mode ? Or can this be tied to > is_kernel_in_hyp_mode() ? Given this mode (from my limited > review) doesn't conflict with normal VHE mode (and RME support), > adding this explicit mode could confuse the user. What is exactly the objection here? NV is more or less a VHE++ mode, but is also completely experimental and incomplete. > In case we need a command line to turn the NV mode on/off, > we could always use the id-override and simply leave this out ? I really want an explicit user buy-in. There is absolutely no way this can be enabled by default, the risks are way too high. Just look at the x86 story: it took them 10 years to enable NV by default. I don't expect to do any better. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel