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[35.233.69.230]) by smtp.gmail.com with ESMTPSA id w25sm5923406wmc.42.2021.02.04.03.08.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 03:08:36 -0800 (PST) Date: Thu, 4 Feb 2021 11:08:33 +0000 From: Quentin Perret To: Will Deacon Cc: Catalin Marinas , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Rob Herring , Frank Rowand , devicetree@vger.kernel.org, android-kvm@google.com, linux-kernel@vger.kernel.org, kernel-team@android.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Fuad Tabba , Mark Rutland , David Brazdil Subject: Re: [RFC PATCH v2 17/26] KVM: arm64: Elevate Hyp mappings creation at EL2 Message-ID: References: <20210108121524.656872-1-qperret@google.com> <20210108121524.656872-18-qperret@google.com> <20210203153138.GB18974@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203153138.GB18974@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 03 Feb 2021 at 15:31:39 (+0000), Will Deacon wrote: > On Fri, Jan 08, 2021 at 12:15:15PM +0000, Quentin Perret wrote: > > Previous commits have introduced infrastructure at EL2 to enable the Hyp > > code to manage its own memory, and more specifically its stage 1 page > > tables. However, this was preliminary work, and none of it is currently > > in use. > > > > Put all of this together by elevating the hyp mappings creation at EL2 > > when memory protection is enabled. In this case, the host kernel running > > at EL1 still creates _temporary_ Hyp mappings, only used while > > initializing the hypervisor, but frees them right after. > > > > As such, all calls to create_hyp_mappings() after kvm init has finished > > turn into hypercalls, as the host now has no 'legal' way to modify the > > hypevisor page tables directly. > > > > Signed-off-by: Quentin Perret > > --- > > arch/arm64/include/asm/kvm_mmu.h | 1 - > > arch/arm64/kvm/arm.c | 62 +++++++++++++++++++++++++++++--- > > arch/arm64/kvm/mmu.c | 34 ++++++++++++++++++ > > 3 files changed, 92 insertions(+), 5 deletions(-) > > > > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h > > index d7ebd73ec86f..6c8466a042a9 100644 > > --- a/arch/arm64/include/asm/kvm_mmu.h > > +++ b/arch/arm64/include/asm/kvm_mmu.h > > @@ -309,6 +309,5 @@ static __always_inline void __load_guest_stage2(struct kvm_s2_mmu *mmu) > > */ > > asm(ALTERNATIVE("nop", "isb", ARM64_WORKAROUND_SPECULATIVE_AT)); > > } > > - > > #endif /* __ASSEMBLY__ */ > > #endif /* __ARM64_KVM_MMU_H__ */ > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index 6af9204bcd5b..e524682c2ccf 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -1421,7 +1421,7 @@ static void cpu_prepare_hyp_mode(int cpu) > > kvm_flush_dcache_to_poc(params, sizeof(*params)); > > } > > > > -static void cpu_init_hyp_mode(void) > > +static void kvm_set_hyp_vector(void) > > Please do something about the naming: now we have both cpu_set_hyp_vector() > and kvm_set_hyp_vector()! I'll try to find something different, but no guarantees it'll be much better :) Suggestions welcome. > > { > > struct kvm_nvhe_init_params *params; > > struct arm_smccc_res res; > > @@ -1439,6 +1439,11 @@ static void cpu_init_hyp_mode(void) > > params = this_cpu_ptr_nvhe_sym(kvm_init_params); > > arm_smccc_1_1_hvc(KVM_HOST_SMCCC_FUNC(__kvm_hyp_init), virt_to_phys(params), &res); > > WARN_ON(res.a0 != SMCCC_RET_SUCCESS); > > +} > > + > > +static void cpu_init_hyp_mode(void) > > +{ > > + kvm_set_hyp_vector(); > > > > /* > > * Disabling SSBD on a non-VHE system requires us to enable SSBS > > @@ -1481,7 +1486,10 @@ static void cpu_set_hyp_vector(void) > > struct bp_hardening_data *data = this_cpu_ptr(&bp_hardening_data); > > void *vector = hyp_spectre_vector_selector[data->slot]; > > > > - *this_cpu_ptr_hyp_sym(kvm_hyp_vector) = (unsigned long)vector; > > + if (!is_protected_kvm_enabled()) > > + *this_cpu_ptr_hyp_sym(kvm_hyp_vector) = (unsigned long)vector; > > + else > > + kvm_call_hyp_nvhe(__pkvm_cpu_set_vector, data->slot); > > *Very* minor nit, but it might be cleaner to have static inline functions > with the same prototypes as the hypercalls, just to make the code even > easier to read. e.g > > if (!is_protected_kvm_enabled()) > _cpu_set_vector(data->slot); > else > kvm_call_hyp_nvhe(__pkvm_cpu_set_vector, data->slot); > > you could then conceivably wrap that in a macro and avoid having the > "is_protected_kvm_enabled()" checks explicit every time. Happy to do this here, but are you suggesting to generalize this pattern to other places as well? > > } > > > > static void cpu_hyp_reinit(void) > > @@ -1489,13 +1497,14 @@ static void cpu_hyp_reinit(void) > > kvm_init_host_cpu_context(&this_cpu_ptr_hyp_sym(kvm_host_data)->host_ctxt); > > > > cpu_hyp_reset(); > > - cpu_set_hyp_vector(); > > > > if (is_kernel_in_hyp_mode()) > > kvm_timer_init_vhe(); > > else > > cpu_init_hyp_mode(); > > > > + cpu_set_hyp_vector(); > > + > > kvm_arm_init_debug(); > > > > if (vgic_present) > > @@ -1714,13 +1723,52 @@ static int copy_cpu_ftr_regs(void) > > return 0; > > } > > > > +static int kvm_hyp_enable_protection(void) > > +{ > > + void *per_cpu_base = kvm_ksym_ref(kvm_arm_hyp_percpu_base); > > + int ret, cpu; > > + void *addr; > > + > > + if (!is_protected_kvm_enabled()) > > + return 0; > > Maybe I'm hung up on my previous suggestion, but I feel like we shouldn't > get here if protected kvm isn't enabled. The alternative is to move this check next to the call site, but it won't help much IMO. > > > + if (!hyp_mem_base) > > + return -ENOMEM; > > + > > + addr = phys_to_virt(hyp_mem_base); > > + ret = create_hyp_mappings(addr, addr + hyp_mem_size - 1, PAGE_HYP); > > + if (ret) > > + return ret; > > + > > + preempt_disable(); > > + kvm_set_hyp_vector(); > > + ret = kvm_call_hyp_nvhe(__pkvm_init, hyp_mem_base, hyp_mem_size, > > + num_possible_cpus(), kern_hyp_va(per_cpu_base)); > > Would it make sense for the __pkvm_init() hypercall to set the vector as > well, so that we wouldn't need to disable preemption over two hypercalls? Not sure, kvm_set_hyp_vector() itself already does multiple hypercalls, and I need it separate from __pkvm_init for secondary CPUs. > Failing that, maybe move the whole preempt_disable/enable sequence into > another function. But that I can do. > > + preempt_enable(); > > + if (ret) > > + return ret; > > + > > + free_hyp_pgds(); > > + for_each_possible_cpu(cpu) > > + free_page(per_cpu(kvm_arm_hyp_stack_page, cpu)); > > + > > + return 0; > > +} > > + > > /** > > * Inits Hyp-mode on all online CPUs > > */ > > static int init_hyp_mode(void) > > { > > int cpu; > > - int err = 0; > > + int err = -ENOMEM; > > + > > + /* > > + * The protected Hyp-mode cannot be initialized if the memory pool > > + * allocation has failed. > > + */ > > + if (is_protected_kvm_enabled() && !hyp_mem_base) > > + return err; > > > > /* > > * Copy the required CPU feature register in their EL2 counterpart > > @@ -1854,6 +1902,12 @@ static int init_hyp_mode(void) > > for_each_possible_cpu(cpu) > > cpu_prepare_hyp_mode(cpu); > > > > + err = kvm_hyp_enable_protection(); > > + if (err) { > > + kvm_err("Failed to enable hyp memory protection: %d\n", err); > > + goto out_err; > > + } > > + > > return 0; > > > > out_err: > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 3cf9397dabdb..9d4c9251208e 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -225,15 +225,39 @@ void free_hyp_pgds(void) > > if (hyp_pgtable) { > > kvm_pgtable_hyp_destroy(hyp_pgtable); > > kfree(hyp_pgtable); > > + hyp_pgtable = NULL; > > } > > mutex_unlock(&kvm_hyp_pgd_mutex); > > } > > > > +static bool kvm_host_owns_hyp_mappings(void) > > +{ > > + if (static_branch_likely(&kvm_protected_mode_initialized)) > > + return false; > > + > > + /* > > + * This can happen at boot time when __create_hyp_mappings() is called > > + * after the hyp protection has been enabled, but the static key has > > + * not been flipped yet. > > + */ > > + if (!hyp_pgtable && is_protected_kvm_enabled()) > > + return false; > > + > > + BUG_ON(!hyp_pgtable); > > Can we fail more gracefully, e.g. by continuing without KVM? Got any suggestion as to how that can be done? We could also just remove that line -- that really should not happen. Thanks! Quentin