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; } return rc; }
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
linux-stable-mirror@lists.linaro.org
-
Christian Borntraeger -
David Hildenbrand