| Message ID | 20200402184819.34215-3-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: vsie: fixes and cleanups. | expand |
On 02.04.20 20:48, David Hildenbrand wrote: > Whenever we get an -EFAULT, we failed to read in guest 2 physical > address space. Such addressing exceptions are reported via a program > intercept to the nested hypervisor. > > We faked the intercept, we have to return to guest 2. Instead, right > now we would be returning -EFAULT from the intercept handler, eventually > crashing the VM. > > Addressing exceptions can only happen if the g2->g3 page tables > reference invalid g2 addresses (say, either a table or the final page is > not accessible - so something that basically never happens in sane > environments. > > Identified by manual code inspection. > > Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") > Cc: <stable@vger.kernel.org> # v4.8+ > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > arch/s390/kvm/vsie.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c > index 076090f9e666..4f6c22d72072 100644 > --- a/arch/s390/kvm/vsie.c > +++ b/arch/s390/kvm/vsie.c > @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) > scb_s->iprcc = PGM_ADDRESSING; > scb_s->pgmilc = 4; > scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); > + rc = 1; kvm_s390_handle_vsie has return rc < 0 ? rc : 0; so rc = 0 would result in the same behaviour, correct? Since we DO handle everything as we should, why rc = 1 ?
On 06.04.20 15:17, Christian Borntraeger wrote: > > > On 02.04.20 20:48, David Hildenbrand wrote: >> Whenever we get an -EFAULT, we failed to read in guest 2 physical >> address space. Such addressing exceptions are reported via a program >> intercept to the nested hypervisor. >> >> We faked the intercept, we have to return to guest 2. Instead, right >> now we would be returning -EFAULT from the intercept handler, eventually >> crashing the VM. >> >> Addressing exceptions can only happen if the g2->g3 page tables >> reference invalid g2 addresses (say, either a table or the final page is >> not accessible - so something that basically never happens in sane >> environments. >> >> Identified by manual code inspection. >> >> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") >> Cc: <stable@vger.kernel.org> # v4.8+ >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> arch/s390/kvm/vsie.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >> index 076090f9e666..4f6c22d72072 100644 >> --- a/arch/s390/kvm/vsie.c >> +++ b/arch/s390/kvm/vsie.c >> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) >> scb_s->iprcc = PGM_ADDRESSING; >> scb_s->pgmilc = 4; >> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); >> + rc = 1; > > > kvm_s390_handle_vsie has > > return rc < 0 ? rc : 0; > > > so rc = 0 would result in the same behaviour, correct? yes > Since we DO handle everything as we should, why rc = 1 ? rc == 1 is the internal representation of "we have to go back into g2". rc == 0, in contrast, means "we can go back into g2 (via a NULL intercept) or continue executing g3". Returning rc == 1 instead of rc == 0 at this point is just consistency.
On 06.04.20 15:22, David Hildenbrand wrote: > On 06.04.20 15:17, Christian Borntraeger wrote: >> >> >> On 02.04.20 20:48, David Hildenbrand wrote: >>> Whenever we get an -EFAULT, we failed to read in guest 2 physical >>> address space. Such addressing exceptions are reported via a program >>> intercept to the nested hypervisor. >>> >>> We faked the intercept, we have to return to guest 2. Instead, right >>> now we would be returning -EFAULT from the intercept handler, eventually >>> crashing the VM. >>> >>> Addressing exceptions can only happen if the g2->g3 page tables >>> reference invalid g2 addresses (say, either a table or the final page is >>> not accessible - so something that basically never happens in sane >>> environments. >>> >>> Identified by manual code inspection. >>> >>> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") >>> Cc: <stable@vger.kernel.org> # v4.8+ >>> Signed-off-by: David Hildenbrand <david@redhat.com> >>> --- >>> arch/s390/kvm/vsie.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >>> index 076090f9e666..4f6c22d72072 100644 >>> --- a/arch/s390/kvm/vsie.c >>> +++ b/arch/s390/kvm/vsie.c >>> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) >>> scb_s->iprcc = PGM_ADDRESSING; >>> scb_s->pgmilc = 4; >>> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); >>> + rc = 1; >> >> >> kvm_s390_handle_vsie has >> >> return rc < 0 ? rc : 0; >> >> >> so rc = 0 would result in the same behaviour, correct? > > yes > >> Since we DO handle everything as we should, why rc = 1 ? > > rc == 1 is the internal representation of "we have to go back into g2". > rc == 0, in contrast, means "we can go back into g2 (via a NULL > intercept) or continue executing g3". Returning rc == 1 instead of rc == > 0 at this point is just consistency. Ok, I will add something to the patch description. Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c index 076090f9e666..4f6c22d72072 100644 --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) scb_s->iprcc = PGM_ADDRESSING; scb_s->pgmilc = 4; scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); + rc = 1; } return rc; }
Whenever we get an -EFAULT, we failed to read in guest 2 physical address space. Such addressing exceptions are reported via a program intercept to the nested hypervisor. We faked the intercept, we have to return to guest 2. Instead, right now we would be returning -EFAULT from the intercept handler, eventually crashing the VM. Addressing exceptions can only happen if the g2->g3 page tables reference invalid g2 addresses (say, either a table or the final page is not accessible - so something that basically never happens in sane environments. Identified by manual code inspection. Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization") Cc: <stable@vger.kernel.org> # v4.8+ Signed-off-by: David Hildenbrand <david@redhat.com> --- arch/s390/kvm/vsie.c | 1 + 1 file changed, 1 insertion(+)