Old kernels did not check for zero in the irq_state.flags field and old
QEMUs did not zero the flag/reserved fields when calling
KVM_S390_*_IRQ_STATE. Let's add comments to prevent future uses of
these fields.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 9 +++++++--
arch/s390/kvm/kvm-s390.c | 2 ++
include/uapi/linux/kvm.h | 4 ++--
3 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index f670e4b..e84c1c3 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2901,14 +2901,19 @@ userspace buffer and its length:
struct kvm_s390_irq_state {
__u64 buf;
- __u32 flags;
+ __u32 flags; /* will be unused for compatibility reasons */
__u32 len;
- __u32 reserved[4];
+ __u32 reserved[4]; /* will be unused for compatibility reasons */
};
Userspace passes in the above struct and for each pending interrupt a
struct kvm_s390_irq is copied to the provided buffer.
+The structure contains a flags and a reserved field for future extensions. As
+the kernel never checked for flags == 0 and QEMU never pre-zeroed flags and
+reserved, these fields can not be used in the future without breaking
+compatibility.
+
If -ENOBUFS is returned the buffer provided was too small and userspace
may retry with a bigger buffer.
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6a5e02f..2a9cc0f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3834,6 +3834,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = -EINVAL;
break;
}
+ /* do not use irq_state.flags, it will break old QEMUs */
r = kvm_s390_set_irq_state(vcpu,
(void __user *) irq_state.buf,
irq_state.len);
@@ -3849,6 +3850,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = -EINVAL;
break;
}
+ /* do not use irq_state.flags, it will break old QEMUs */
r = kvm_s390_get_irq_state(vcpu,
(__u8 __user *) irq_state.buf,
irq_state.len);
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 282d7613..6f91b41 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -630,9 +630,9 @@ struct kvm_s390_irq {
struct kvm_s390_irq_state {
__u64 buf;
- __u32 flags;
+ __u32 flags; /* will be unused for compatibility reasons */
__u32 len;
- __u32 reserved[4];
+ __u32 reserved[4]; /* will be unused for compatibility reasons */
};
/* for KVM_SET_GUEST_DEBUG */
--
2.9.4
--
To unsubscribe from this list: send the line "unsubscribe linux-s390" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
