From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 06/14] KVM: arm/arm64: Factor out VMID into struct kvm_vmid Date: Thu, 21 Feb 2019 11:02:56 +0000 Message-ID: <1978ee57-c7bd-e55a-4e77-ad0b4b62d1d1@arm.com> References: <20190124140032.8588-1-christoffer.dall@arm.com> <20190124140032.8588-7-christoffer.dall@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Marc Zyngier , nd , "kvm@vger.kernel.org" To: Christoffer Dall , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" Return-path: In-Reply-To: <20190124140032.8588-7-christoffer.dall@arm.com> Content-Language: en-US Content-ID: <7E8DC60B4CA826488988D8D2B3C89E0B@eurprd08.prod.outlook.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org Hi Christoffer, On 24/01/2019 14:00, Christoffer Dall wrote: > Note that to avoid mapping the kvm_vmid_bits variable into hyp, we > simply forego the masking of the vmid value in kvm_get_vttbr and rely on > update_vmid to always assign a valid vmid value (within the supported > range). [...] > - kvm->arch.vmid = kvm_next_vmid; > + vmid->vmid = kvm_next_vmid; > kvm_next_vmid++; > - kvm_next_vmid &= (1 << kvm_vmid_bits) - 1; > - > - /* update vttbr to be used with the new vmid */ > - pgd_phys = virt_to_phys(kvm->arch.pgd); > - BUG_ON(pgd_phys & ~kvm_vttbr_baddr_mask(kvm)); > - vmid = ((u64)(kvm->arch.vmid) << VTTBR_VMID_SHIFT) & VTTBR_VMID_MASK(kvm_vmid_bits); > - kvm->arch.vttbr = kvm_phys_to_vttbr(pgd_phys) | vmid | cnp; > + kvm_next_vmid &= (1 << kvm_get_vmid_bits()) - 1; The arm64 version of kvm_get_vmid_bits does not look cheap. Indeed it required to read the sanitized value of SYS_ID_AA64MMFR1_EL1 that is implemented using the function bsearch. So wouldn't it be better to keep kvm_vmid_bits variable for use in update_vttbr()? Cheers, -- Julien Grall