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From: Oliver Upton To: Sebastian Ott Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Marc Zyngier , James Morse , Suzuki K Poulose , Catalin Marinas , Will Deacon , Shaoqin Huang , Eric Auger Subject: Re: [PATCH v4 3/6] KVM: arm64: add emulation for CTR_EL0 register Message-ID: References: <20240603130507.17597-1-sebott@redhat.com> <20240603130507.17597-4-sebott@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240613_153026_088570_DD12794B X-CRM114-Status: GOOD ( 21.42 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jun 13, 2024 at 10:19:56PM +0000, Oliver Upton wrote: > Hi Sebastian, > > On Mon, Jun 03, 2024 at 03:05:04PM +0200, Sebastian Ott wrote: > > [...] > > > +static int validate_cache_topology(struct kvm_vcpu *vcpu, u64 ctr_el0) > > +{ > > + const struct sys_reg_desc *clidr_el1; > > + unsigned int i; > > + int ret; > > + > > + clidr_el1 = get_sys_reg_desc(SYS_CLIDR_EL1); > > + if (!clidr_el1) > > + return -ENOENT; > > This doesn't actually matter if we agree on dropping the cross-checking, > but if this lookup fails it is 100% a KVM bug. Returning ENOENT isn't > exactly right here, since it gives userspace the impression that the > sysreg index it tried to access does not exist. > > So in the future it'd be good to return EINVAL in places where the > kernel did something stupid, probably with a warning for good measure. > > > +static int set_ctr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > + u64 val) > > +{ > > + u64 ctr, writable_mask = rd->val; > > + int ret = 0; > > + > > + mutex_lock(&vcpu->kvm->arch.config_lock); > > + ctr = vcpu->kvm->arch.ctr_el0; > > + if (val == ctr) > > + goto out_unlock; > > + > > + ret = -EBUSY; > > + if (kvm_vm_has_ran_once(vcpu->kvm)) > > + goto out_unlock; > > + > > + ret = -EINVAL; > > + if ((ctr & ~writable_mask) != (val & ~writable_mask)) > > + goto out_unlock; > > + > > + if (((ctr & CTR_EL0_DIC_MASK) < (val & CTR_EL0_DIC_MASK)) || > > + ((ctr & CTR_EL0_IDC_MASK) < (val & CTR_EL0_IDC_MASK)) || > > + ((ctr & CTR_EL0_DminLine_MASK) < (val & CTR_EL0_DminLine_MASK)) || > > + ((ctr & CTR_EL0_IminLine_MASK) < (val & CTR_EL0_IminLine_MASK))) { > > + goto out_unlock; > > I'd prefer if we addressed the issue w/ arm64_check_features() by making > CTR_EL0 behave like the other registers in the ID space instead of > open-coding these sorts of checks. > > I believe that can be accomplished by using kvm_read_sanitised_id_reg() > as the ::reset() function in the descriptor and initializing > kvm->arch.ctr_el0 in kvm_reset_id_regs(). Durr, I got rid of kvm_reset_id_regs() in commit 44cbe80b7616 ("KVM: arm64: Reset VM feature ID regs from kvm_reset_sys_regs()"), I should engage brain before responding. Adding a check for encoding == CTR_EL0 to is_vm_ftr_id_reg() seems to be the best way out. -- Thanks, Oliver