| Message ID | 20171121150806.47075-1-borntraeger@de.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 21.11.2017 16:08, Christian Borntraeger wrote: > Old kernels did not check for zero in the irq_state.flags field and old > QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE. > Let's add a comment and dummy code to prevent future usage of flags > and pad. > > Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> > --- > arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 6a5e02f..1baa393 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > r = -EINVAL; > break; > } > + if (irq_state.flags) { I don't see the need for if (do I need more coffee?). > + /* > + * This is a placeholder to make sure that nobody uses > + * flags and pad. Old kernels did not check for zero > + * and old QEMUs did not zero the flag field. > + * That means that we cannot use the flags field for > + * any possible extension. > + */ > + irq_state.flags = 0; > + } > r = kvm_s390_set_irq_state(vcpu, > (void __user *) irq_state.buf, > irq_state.len); > @@ -3849,6 +3859,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > r = -EINVAL; > break; > } > + if (irq_state.flags) { dito > + /* see above */ /* same handling as for kvm_s390_set_irq_state() */ > + irq_state.flags = 0; > + } > r = kvm_s390_get_irq_state(vcpu, > (__u8 __user *) irq_state.buf, > irq_state.len); >
On Tue, 21 Nov 2017 16:18:53 +0100 David Hildenbrand <david@redhat.com> wrote: > On 21.11.2017 16:08, Christian Borntraeger wrote: > > Old kernels did not check for zero in the irq_state.flags field and old > > QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE. > > Let's add a comment and dummy code to prevent future usage of flags > > and pad. > > > > Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> > > --- > > arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > > index 6a5e02f..1baa393 100644 > > --- a/arch/s390/kvm/kvm-s390.c > > +++ b/arch/s390/kvm/kvm-s390.c > > @@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > > r = -EINVAL; > > break; > > } > > + if (irq_state.flags) { > > I don't see the need for if (do I need more coffee?). I think the if can be dropped and flags zeroed unconditionally, as we can't do anything special for flags != 0 anyway. > > > + /* > > + * This is a placeholder to make sure that nobody uses > > + * flags and pad. Old kernels did not check for zero > > + * and old QEMUs did not zero the flag field. > > + * That means that we cannot use the flags field for > > + * any possible extension. > > + */ > > + irq_state.flags = 0; > > + } > > r = kvm_s390_set_irq_state(vcpu, > > (void __user *) irq_state.buf, > > irq_state.len); > > @@ -3849,6 +3859,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > > r = -EINVAL; > > break; > > } > > + if (irq_state.flags) { > > dito > > > + /* see above */ > > /* same handling as for kvm_s390_set_irq_state() */ I like that comment better. > > > + irq_state.flags = 0; > > + } > > r = kvm_s390_get_irq_state(vcpu, > > (__u8 __user *) irq_state.buf, > > irq_state.len); > > > > We should also document this in Documentation/virtual/kvm/api.txt, I think. (Checking, the documentation for set_irq_state also seems wrong.)
On 11/21/2017 04:18 PM, David Hildenbrand wrote: > On 21.11.2017 16:08, Christian Borntraeger wrote: >> Old kernels did not check for zero in the irq_state.flags field and old >> QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE. >> Let's add a comment and dummy code to prevent future usage of flags >> and pad. >> >> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> >> --- >> arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 6a5e02f..1baa393 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp, >> r = -EINVAL; >> break; >> } >> + if (irq_state.flags) { > > I don't see the need for if (do I need more coffee?). It is a dummy construct that matches other checks like "if flags return -EINVAL". But since it is dummy we can do whatever we want (even just a comment) since nobody reads flags as of today. > >> + /* >> + * This is a placeholder to make sure that nobody uses >> + * flags and pad. Old kernels did not check for zero >> + * and old QEMUs did not zero the flag field. >> + * That means that we cannot use the flags field for >> + * any possible extension. >> + */ >> + irq_state.flags = 0; >> + } >> r = kvm_s390_set_irq_state(vcpu, >> (void __user *) irq_state.buf, >> irq_state.len); >> @@ -3849,6 +3859,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, >> r = -EINVAL; >> break; >> } >> + if (irq_state.flags) { > > dito > >> + /* see above */ > > /* same handling as for kvm_s390_set_irq_state() */ > >> + irq_state.flags = 0; >> + } >> r = kvm_s390_get_irq_state(vcpu, >> (__u8 __user *) irq_state.buf, >> irq_state.len); >> > >
On 21.11.2017 18:42, Christian Borntraeger wrote: > > > On 11/21/2017 04:18 PM, David Hildenbrand wrote: >> On 21.11.2017 16:08, Christian Borntraeger wrote: >>> Old kernels did not check for zero in the irq_state.flags field and old >>> QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE. >>> Let's add a comment and dummy code to prevent future usage of flags >>> and pad. >>> >>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> >>> --- >>> arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++ >>> 1 file changed, 14 insertions(+) >>> >>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>> index 6a5e02f..1baa393 100644 >>> --- a/arch/s390/kvm/kvm-s390.c >>> +++ b/arch/s390/kvm/kvm-s390.c >>> @@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp, >>> r = -EINVAL; >>> break; >>> } >>> + if (irq_state.flags) { >> >> I don't see the need for if (do I need more coffee?). > > It is a dummy construct that matches other checks like "if flags return -EINVAL". But since > it is dummy we can do whatever we want (even just a comment) since nobody reads flags as of > today. Not sure if changing the code here really makes sense ... I think I'd rather prefer to add a comment to the header where the struct is defined, and add some proper sentences about "flags" to the api.txt file. Thomas
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 6a5e02f..1baa393 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp, r = -EINVAL; break; } + if (irq_state.flags) { + /* + * This is a placeholder to make sure that nobody uses + * flags and pad. Old kernels did not check for zero + * and old QEMUs did not zero the flag field. + * That means that we cannot use the flags field for + * any possible extension. + */ + irq_state.flags = 0; + } r = kvm_s390_set_irq_state(vcpu, (void __user *) irq_state.buf, irq_state.len); @@ -3849,6 +3859,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, r = -EINVAL; break; } + if (irq_state.flags) { + /* see above */ + irq_state.flags = 0; + } r = kvm_s390_get_irq_state(vcpu, (__u8 __user *) irq_state.buf, irq_state.len);
Old kernels did not check for zero in the irq_state.flags field and old QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE. Let's add a comment and dummy code to prevent future usage of flags and pad. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> --- arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)