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[34.140.183.197]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1d85f92d9sm190610495e9.4.2026.10.19.03.00.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Oct 2026 03:00:19 -0700 (PDT) Date: Mon, 19 Oct 2026 11:00:15 +0100 From: Vincent Donnefort To: Fuad Tabba Cc: Marc Zyngier , Oliver Upton , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Quentin Perret , Fuad Tabba , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] KVM: arm64: Ensure TLBs and I-cache are private to each vCPU in pKVM Message-ID: References: <20261014125510.2928306-1-fuad.tabba@linux.dev> <20261014125510.2928306-3-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261014125510.2928306-3-fuad.tabba@linux.dev> On Wed, Oct 14, 2026 at 01:55:10PM +0100, Fuad Tabba wrote: > All vCPUs of a VM share its VMID, so KVM flushes a physical CPU's TLBs > and I-cache for the VM whenever a different vCPU of that VM is loaded > there (vcpu_prepare_mmu()). Commit fce886a602073 ("KVM: arm64: Plumb the > pKVM MMU in KVM") moved pKVM guests, protected or not, onto the > hypervisor's stage-2 and VMID, and the host stopped flushing for them. > Nothing at EL2 flushes instead, so a vCPU can hit TLB and I-cache > entries that another vCPU of the same VM left on that CPU. > > Track the last vCPU loaded on each physical CPU in the hyp VM, and flush > at EL2 in __pkvm_vcpu_load() when it changes. > > Fixes: fce886a602073 ("KVM: arm64: Plumb the pKVM MMU in KVM") > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/include/nvhe/pkvm.h | 3 +++ > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 8 ++++++++ > arch/arm64/kvm/hyp/nvhe/pkvm.c | 21 ++++++++++++++++++--- > 3 files changed, 29 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h > index 9abfe6b7e942b..02c8fc7a10904 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h > @@ -54,6 +54,9 @@ struct pkvm_hyp_vm { > unsigned short refcount; > hyp_spinlock_t lock; > > + /* Per physical CPU, the vcpu_idx of the last vCPU of this VM loaded there. */ > + int *last_vcpu_ran; Unlikely to be a problem in pratice, but vcpu_idx is "unsigned int". I wonder if this shouldn't be unsigned int here too and initialised to UINT_MAX? > + > /* > * The vCPU initialised RUNNABLE: claimed under vm_table_lock, > * released only if its own init fails. > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index d715aa942577e..f0b77236c871e 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -827,11 +827,19 @@ DEFINE_KVM_HOST_HCALL(void, __pkvm_vcpu_load, > pkvm_handle_t, handle, unsigned int, vcpu_idx, u64, hcr_el2) > { > struct pkvm_hyp_vcpu *hyp_vcpu; > + int *last_ran; > > hyp_vcpu = pkvm_load_hyp_vcpu(handle, vcpu_idx); > if (!hyp_vcpu) > return; > > + /* TLBs and I-cache are private to each vCPU, see vcpu_prepare_mmu(). */ > + last_ran = &pkvm_hyp_vcpu_to_hyp_vm(hyp_vcpu)->last_vcpu_ran[hyp_smp_processor_id()]; > + if (*last_ran != vcpu_idx) { > + __kvm_flush_cpu_context(hyp_vcpu->vcpu.arch.hw_mmu); > + *last_ran = vcpu_idx; > + } > + > if (pkvm_hyp_vcpu_is_protected(hyp_vcpu)) { > u64 dfr0 = read_sysreg(id_aa64dfr0_el1); > > diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c > index ac020d0501d2e..f18fa762746c9 100644 > --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c > +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c > @@ -489,10 +489,11 @@ static void unpin_host_vcpus(struct pkvm_hyp_vcpu *hyp_vcpus[], > } > > static void init_pkvm_hyp_vm(struct kvm *host_kvm, struct pkvm_hyp_vm *hyp_vm, > - unsigned int nr_vcpus, pkvm_handle_t handle) > + int *last_vcpu_ran, unsigned int nr_vcpus, pkvm_handle_t handle) > { > struct kvm_s2_mmu *mmu = &hyp_vm->kvm.arch.mmu; > int idx = vm_handle_to_idx(handle); > + unsigned long cpu; > > hyp_vm->kvm.arch.pkvm.handle = handle; > > @@ -512,6 +513,10 @@ static void init_pkvm_hyp_vm(struct kvm *host_kvm, struct pkvm_hyp_vm *hyp_vm, > mmu->vtcr = host_mmu.arch.mmu.vtcr; > mmu->arch = &hyp_vm->kvm.arch; > mmu->pgt = &hyp_vm->pgt; > + > + for (cpu = 0; cpu < hyp_nr_cpus; cpu++) > + last_vcpu_ran[cpu] = -1; > + hyp_vm->last_vcpu_ran = last_vcpu_ran; > } > > static int pkvm_vcpu_init_sve(struct pkvm_hyp_vcpu *hyp_vcpu, struct kvm_vcpu *host_vcpu) > @@ -887,6 +892,7 @@ int __pkvm_init_vm(struct kvm *host_kvm, void __kern *pgd_hva) > size_t vm_size, pgd_size; > unsigned int nr_vcpus; > pkvm_handle_t handle; > + int *last_vcpu_ran; > void *pgd = NULL; > int ret; > > @@ -915,13 +921,19 @@ int __pkvm_init_vm(struct kvm *host_kvm, void __kern *pgd_hva) > goto err_unpin_kvm; > } > > + last_vcpu_ran = hyp_alloc(array_size(hyp_nr_cpus, sizeof(*last_vcpu_ran))); > + if (!last_vcpu_ran) { > + ret = hyp_alloc_errno(); > + goto err_free_hyp_vm; > + } > + > ret = -ENOMEM; > > pgd = map_donated_memory_noclear(pgd_hva, pgd_size); > if (!pgd) > - goto err_free_hyp_vm; > + goto err_free_last_ran; > > - init_pkvm_hyp_vm(host_kvm, hyp_vm, nr_vcpus, handle); > + init_pkvm_hyp_vm(host_kvm, hyp_vm, last_vcpu_ran, nr_vcpus, handle); > > ret = kvm_guest_prepare_stage2(hyp_vm, pgd); > if (ret) > @@ -938,6 +950,8 @@ int __pkvm_init_vm(struct kvm *host_kvm, void __kern *pgd_hva) > kvm_guest_destroy_stage2(hyp_vm); > err_remove_mappings: > unmap_donated_memory(pgd, pgd_size); > +err_free_last_ran: > + hyp_free(last_vcpu_ran); > err_free_hyp_vm: > hyp_free(hyp_vm); > err_unpin_kvm: > @@ -1112,6 +1126,7 @@ int __pkvm_finalize_teardown_vm(pkvm_handle_t handle) > hyp_free(hyp_vcpu); > } > > + hyp_free(hyp_vm->last_vcpu_ran); > hyp_free(hyp_vm); > hyp_unpin_shared_mem(host_kvm, host_kvm + 1); > return 0; > -- > 2.39.5 >