Messages in this thread | | | Subject | Re: [PATCH 6/7] KVM: arm64: Change return type of kvm_vm_ioctl_mte_copy_tags() to "int" | From | Gavin Shan <> | Date | Wed, 8 Feb 2023 09:16:36 +1100 |
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On 2/7/23 9:09 PM, Thomas Huth wrote: > On 07/02/2023 01.09, Gavin Shan wrote: >> Hi Thomas, >> >> On 2/3/23 8:42 PM, Thomas Huth wrote: >>> This function only returns normal integer values, so there is >>> no need to declare its return value as "long". >>> >>> Signed-off-by: Thomas Huth <thuth@redhat.com> >>> --- >>> arch/arm64/include/asm/kvm_host.h | 4 ++-- >>> arch/arm64/kvm/guest.c | 4 ++-- >>> 2 files changed, 4 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >>> index 35a159d131b5..b1a16343767f 100644 >>> --- a/arch/arm64/include/asm/kvm_host.h >>> +++ b/arch/arm64/include/asm/kvm_host.h >>> @@ -963,8 +963,8 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu, >>> int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu, >>> struct kvm_device_attr *attr); >>> -long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >>> - struct kvm_arm_copy_mte_tags *copy_tags); >>> +int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >>> + struct kvm_arm_copy_mte_tags *copy_tags); >>> /* Guest/host FPSIMD coordination helpers */ >>> int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu); >>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c >>> index cf4c495a4321..80e530549c34 100644 >>> --- a/arch/arm64/kvm/guest.c >>> +++ b/arch/arm64/kvm/guest.c >>> @@ -1013,8 +1013,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu, >>> return ret; >>> } >>> -long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >>> - struct kvm_arm_copy_mte_tags *copy_tags) >>> +int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >>> + struct kvm_arm_copy_mte_tags *copy_tags) >>> { >>> gpa_t guest_ipa = copy_tags->guest_ipa; >>> size_t length = copy_tags->length; >>> >> >> It's possible for the function to return number of bytes have been copied. >> Its type is 'size_t', same to 'unsigned long'. So 'int' doesn't have sufficient >> space for it if I'm correct. >> >> long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> struct kvm_arm_copy_mte_tags *copy_tags) >> { >> gpa_t guest_ipa = copy_tags->guest_ipa; >> size_t length = copy_tags->length; >> : >> : >> out: >> mutex_unlock(&kvm->slots_lock); >> /* If some data has been copied report the number of bytes copied */ >> if (length != copy_tags->length) >> return copy_tags->length - length; >> return ret; >> } > > Oh, drat, I thought I had checked all return statements ... this must have fallen through the cracks, sorry! > > Anyway, this is already a problem now: The function is called from kvm_arch_vm_ioctl() (which still returns a long), which in turn is called from kvm_vm_ioctl() in virt/kvm/kvm_main.c. And that functions stores the return value in an "int r" variable. So the upper bits are already lost there. > > Also, how is this supposed to work from user space? The normal "ioctl()" libc function just returns an "int" ? Is this ioctl already used in a userspace application somewhere? ... at least in QEMU, I didn't spot it yet... >
The ioctl command KVM_ARM_MTE_COPY_TAGS was merged recently and not used by QEMU yet. I think struct kvm_arm_copy_mte_tags::length needs to be '__u32' instead of '__u64' in order to standardize the return value. Something like below. Documentation/virt/kvm/api.rst::section-4.130 needs update accordingly.
struct kvm_arm_copy_mte_tags { __u64 guest_ipa; __u32 pad; __u32 length; void __user *addr; __u64 flags; __u64 reserved[2]; };
Thanks, Gavin
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