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Mon, 29 Sep 2025 06:59:37 -0700 (PDT) Message-ID: <7d109638-3d26-443a-b24d-eb7a0059b80f@gmail.com> Date: Mon, 29 Sep 2025 14:59:35 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/6] KVM: arm64: Add pre_fault_memory implementation Content-Language: en-GB To: Oliver Upton Cc: maz@kernel.org, pbonzini@redhat.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, isaku.yamahata@intel.com, roypat@amazon.co.uk, kalyazin@amazon.co.uk, jackabt@amazon.com References: <20250911134648.58945-1-jackabt.amazon@gmail.com> <20250911134648.58945-4-jackabt.amazon@gmail.com> From: "Thomson, Jack" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Oliver, Thanks for reviewing! On 11/09/2025 7:42 pm, Oliver Upton wrote: > On Thu, Sep 11, 2025 at 02:46:45PM +0100, Jack Thomson wrote: >> @@ -1607,7 +1611,7 @@ static int __user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> struct kvm_s2_trans *nested, >> struct kvm_memory_slot *memslot, >> long *page_size, unsigned long hva, >> - bool fault_is_perm) >> + bool fault_is_perm, bool pre_fault) >> { >> int ret = 0; >> bool topup_memcache; >> @@ -1631,10 +1635,13 @@ static int __user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> vm_flags_t vm_flags; >> enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_MEMABORT_FLAGS; >> >> + if (pre_fault) >> + flags |= KVM_PGTABLE_WALK_PRE_FAULT; >> + >> if (fault_is_perm) >> fault_granule = kvm_vcpu_trap_get_perm_fault_granule(vcpu); >> - write_fault = kvm_is_write_fault(vcpu); >> - exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu); >> + write_fault = !pre_fault && kvm_is_write_fault(vcpu); >> + exec_fault = !pre_fault && kvm_vcpu_trap_is_exec_fault(vcpu); > > I'm not a fan of this. While user_mem_abort() is already a sloppy mess, > one thing we could reliably assume is the presence of a valid fault > context. Now we need to remember to special-case our interpretation of a > fault on whether or not we're getting invoked for a pre-fault. > > I'd rather see the pre-fault infrastructure compose a synthetic fault > context (HPFAR_EL2, ESR_EL2, etc.). It places the complexity where it > belongs and the rest of the abort handling code should 'just work'. > Agreed, it looks much better with the synthetic abort. Is this the approach you had in mind? +long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, + struct kvm_pre_fault_memory *range) +{ + int ret, idx; + hva_t hva; + phys_addr_t end; + u64 esr, hpfar; + struct kvm_memory_slot *memslot; + struct kvm_vcpu_fault_info *fault_info; + + long page_size = PAGE_SIZE; + phys_addr_t ipa = range->gpa; + gfn_t gfn = gpa_to_gfn(range->gpa); + + idx = srcu_read_lock(&vcpu->kvm->srcu); + + if (ipa >= kvm_phys_size(vcpu->arch.hw_mmu)) { + ret = -ENOENT; + goto out_unlock; + } + + memslot = gfn_to_memslot(vcpu->kvm, gfn); + if (!memslot) { + ret = -ENOENT; + goto out_unlock; + } + + fault_info = &vcpu->arch.fault; + + esr = fault_info->esr_el2; + hpfar = fault_info->hpfar_el2; + + fault_info->esr_el2 = ESR_ELx_FSC_ACCESS_L(KVM_PGTABLE_LAST_LEVEL); + fault_info->hpfar_el2 = HPFAR_EL2_NS | + ((ipa >> (12 - HPFAR_EL2_FIPA_SHIFT)) & HPFAR_EL2_FIPA_MASK); + + if (kvm_slot_has_gmem(memslot)) { + ret = gmem_abort(vcpu, ipa, NULL, memslot, false); + } else { + hva = gfn_to_hva_memslot_prot(memslot, gfn, NULL); + if (kvm_is_error_hva(hva)) { + ret = -EFAULT; + goto out; + } + ret = user_mem_abort(vcpu, ipa, NULL, memslot, &page_size, hva, + false); + } + + if (ret < 0) + goto out; + + end = (range->gpa & ~(page_size - 1)) + page_size; + ret = min(range->size, end - range->gpa); + +out: + fault_info->esr_el2 = esr; + fault_info->hpfar_el2 = hpfar; +out_unlock: + srcu_read_unlock(&vcpu->kvm->srcu, idx); + return ret; +} >> +long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, >> + struct kvm_pre_fault_memory *range) >> +{ >> + int r; >> + hva_t hva; >> + phys_addr_t end; >> + long page_size; >> + struct kvm_memory_slot *memslot; >> + phys_addr_t ipa = range->gpa; >> + gfn_t gfn = gpa_to_gfn(range->gpa); >> + >> + while (true) { >> + page_size = PAGE_SIZE; >> + memslot = gfn_to_memslot(vcpu->kvm, gfn); >> + if (!memslot) >> + return -ENOENT; >> + >> + if (kvm_slot_has_gmem(memslot)) { >> + r = __gmem_abort(vcpu, ipa, NULL, memslot, false, true); >> + } else { >> + hva = gfn_to_hva_memslot_prot(memslot, gfn, NULL); >> + if (kvm_is_error_hva(hva)) >> + return -EFAULT; >> + r = __user_mem_abort(vcpu, ipa, NULL, memslot, &page_size, hva, false, >> + true); >> + } >> + >> + if (r != -EAGAIN) >> + break; >> + >> + if (signal_pending(current)) >> + return -EINTR; >> + >> + if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) >> + return -EIO; >> + >> + cond_resched(); >> + }; > > Why do we need another retry loop? Looks like we've already got one in > the arch-generic code. > Good point thanks, I've removed that now. > > Thanks, > Oliver Thanks, Jack