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Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Thiago Jung Bauermann , Ross Burton , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, joey.gouly@arm.com Subject: Re: [PATCH v10 14/40] KVM: arm64: Manage GCS access and registers for guests In-Reply-To: <8c1e8fb6-0152-42f7-ab6d-93f6fe70b4aa@sirena.org.uk> References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org> <20240801-arm64-gcs-v10-14-699e2bd2190b@kernel.org> <86h6bkzh8o.wl-maz@kernel.org> <8c1e8fb6-0152-42f7-ab6d-93f6fe70b4aa@sirena.org.uk> 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/29.4 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: broonie@kernel.org, catalin.marinas@arm.com, will@kernel.org, corbet@lwn.net, akpm@linux-foundation.org, oliver.upton@linux.dev, james.morse@arm.com, suzuki.poulose@arm.com, arnd@arndb.de, oleg@redhat.com, ebiederm@xmission.com, shuah@kernel.org, rick.p.edgecombe@intel.com, debug@rivosinc.com, ardb@kernel.org, Szabolcs.Nagy@arm.com, kees@kernel.org, hjl.tools@gmail.com, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, fweimer@redhat.com, brauner@kernel.org, thiago.bauermann@linaro.org, ross.burton@arm.com, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, joey.gouly@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-Rspam-User: X-Stat-Signature: ohoficx993daudfwysqyj8hiozyze6nr X-Rspamd-Queue-Id: 415B0140003 X-Rspamd-Server: rspam11 X-HE-Tag: 1723819925-850372 X-HE-Meta: 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 oRrzyXft Uj/qU+Ove9Dy1AIYHHWT53PmsWCrhJcVfCTeNP86Jl18fabYM5dwjcBypV+9mLgCLK4MrMKRihncM2CSXvTlHNYDSULEbTDMEZ8C0YXpXDVHQFK2BUF/jx7V+vSojWKfTGX6Boa5Bu6C60MmSdyc/0P99v16fXOwyPFZVLe7btr43E4zN7l1c8xCHmmDekFqV4AbcHv97CugAdZs2s4emAdKdKUtoVIXYVBC4L5Zt+bjFgSUTq+4b+DrVBx6ccQT6WCukVb2XmeCFldio9sx76uE3rvD6H5lY3qSZpnL2xRj9oVf0WBnmC0+MNAYFsWj+VkqHBynLjQyd0C4QDj9TASS+Kpx743h+Kgcmqn5gd3Sbkncc6ZNb90xCZgm+1MsRQuaa X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 16 Aug 2024 15:40:33 +0100, Mark Brown wrote: > > [1 ] > On Fri, Aug 16, 2024 at 03:15:19PM +0100, Marc Zyngier wrote: > > Mark Brown wrote: > > > > + { SYS_DESC(SYS_GCSCR_EL1), NULL, reset_val, GCSCR_EL1, 0 }, > > > + { SYS_DESC(SYS_GCSPR_EL1), NULL, reset_unknown, GCSPR_EL1 }, > > > + { SYS_DESC(SYS_GCSCRE0_EL1), NULL, reset_val, GCSCRE0_EL1, 0 }, > > > Global visibility for these registers? Why should we expose them to > > userspace if the feature is neither present nor configured? > > ... > > > > + if (!kvm_has_feat(kvm, ID_AA64PFR1_EL1, GCS, IMP)) > > > + kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 | > > > + HFGxTR_EL2_nGCS_EL1); > > > How can this work if you don't handle ID_AA64PFR_EL1 being written to? > > You are exposing GCS to all guests without giving the VMM an > > opportunity to turn it off. This breaks A->B->A migration, which is > > not acceptable. > > This was done based on your positive review of the POE series which > follows the same pattern: > > https://lore.kernel.org/linux-arm-kernel/20240503130147.1154804-8-joey.gouly@arm.com/ > https://lore.kernel.org/linux-arm-kernel/864jagmxn7.wl-maz@kernel.org/ > > in which you didn't note any concerns about the handling for the > sysregs. > > If your decisions have changed then you'll need to withdraw your review > there, I'd figured that given the current incompleteness of the > writability conversions and there being a bunch of existing registers > exposed unconditionally you'd decided to defer until some more general > cleanup of the situation. Thanks for pointing out that I missed this crucial detail in the POE series. I'll immediately go and point that out. M. -- Without deviation from the norm, progress is not possible.