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@xxxxxxxxxx>
---
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
