* Re: [PATCH] KVM: s390: fix guarded storage control register handling
2021-04-15 8:01 [PATCH] KVM: s390: fix guarded storage control register handling Heiko Carstens
@ 2021-04-15 8:35 ` David Hildenbrand
2021-04-15 8:39 ` Janosch Frank
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: David Hildenbrand @ 2021-04-15 8:35 UTC (permalink / raw)
To: Heiko Carstens, Christian Borntraeger, Janosch Frank
Cc: Cornelia Huck, Claudio Imbrenda, kvm, linux-s390
On 15.04.21 10:01, Heiko Carstens wrote:
> store_regs_fmt2() has an ordering problem: first the guarded storage
> facility is enabled on the local cpu, then preemption disabled, and
> then the STGSC (store guarded storage controls) instruction is
> executed.
>
> If the process gets scheduled away between enabling the guarded
> storage facility and before preemption is disabled, this might lead to
> a special operation exception and therefore kernel crash as soon as
> the process is scheduled back and the STGSC instruction is executed.
>
> Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests")
> Cc: <stable@vger.kernel.org> # 4.12
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 2f09e9d7dc95..24ad447e648c 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4307,16 +4307,16 @@ static void store_regs_fmt2(struct kvm_vcpu *vcpu)
> kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
> kvm_run->s.regs.diag318 = vcpu->arch.diag318_info.val;
> if (MACHINE_HAS_GS) {
> + preempt_disable();
> __ctl_set_bit(2, 4);
> if (vcpu->arch.gs_enabled)
> save_gs_cb(current->thread.gs_cb);
> - preempt_disable();
> current->thread.gs_cb = vcpu->arch.host_gscb;
> restore_gs_cb(vcpu->arch.host_gscb);
> - preempt_enable();
> if (!vcpu->arch.host_gscb)
> __ctl_clear_bit(2, 4);
> vcpu->arch.host_gscb = NULL;
> + preempt_enable();
> }
> /* SIE will save etoken directly into SDNX and therefore kvm_run */
> }
>
LGTM
Reviewed-by: David Hildenbrand <david@redhat.com>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: s390: fix guarded storage control register handling
2021-04-15 8:01 [PATCH] KVM: s390: fix guarded storage control register handling Heiko Carstens
2021-04-15 8:35 ` David Hildenbrand
@ 2021-04-15 8:39 ` Janosch Frank
2021-04-15 9:01 ` Cornelia Huck
2021-04-15 10:50 ` Christian Borntraeger
3 siblings, 0 replies; 5+ messages in thread
From: Janosch Frank @ 2021-04-15 8:39 UTC (permalink / raw)
To: Heiko Carstens, Christian Borntraeger, Janosch Frank
Cc: David Hildenbrand, Cornelia Huck, Claudio Imbrenda, kvm, linux-s390
On 4/15/21 10:01 AM, Heiko Carstens wrote:
> store_regs_fmt2() has an ordering problem: first the guarded storage
> facility is enabled on the local cpu, then preemption disabled, and
> then the STGSC (store guarded storage controls) instruction is
> executed.
>
> If the process gets scheduled away between enabling the guarded
> storage facility and before preemption is disabled, this might lead to
> a special operation exception and therefore kernel crash as soon as
> the process is scheduled back and the STGSC instruction is executed.
>
> Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests")
> Cc: <stable@vger.kernel.org> # 4.12
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 2f09e9d7dc95..24ad447e648c 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4307,16 +4307,16 @@ static void store_regs_fmt2(struct kvm_vcpu *vcpu)
> kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
> kvm_run->s.regs.diag318 = vcpu->arch.diag318_info.val;
> if (MACHINE_HAS_GS) {
> + preempt_disable();
> __ctl_set_bit(2, 4);
> if (vcpu->arch.gs_enabled)
> save_gs_cb(current->thread.gs_cb);
> - preempt_disable();
> current->thread.gs_cb = vcpu->arch.host_gscb;
> restore_gs_cb(vcpu->arch.host_gscb);
> - preempt_enable();
> if (!vcpu->arch.host_gscb)
> __ctl_clear_bit(2, 4);
> vcpu->arch.host_gscb = NULL;
> + preempt_enable();
> }
> /* SIE will save etoken directly into SDNX and therefore kvm_run */
> }
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: s390: fix guarded storage control register handling
2021-04-15 8:01 [PATCH] KVM: s390: fix guarded storage control register handling Heiko Carstens
2021-04-15 8:35 ` David Hildenbrand
2021-04-15 8:39 ` Janosch Frank
@ 2021-04-15 9:01 ` Cornelia Huck
2021-04-15 10:50 ` Christian Borntraeger
3 siblings, 0 replies; 5+ messages in thread
From: Cornelia Huck @ 2021-04-15 9:01 UTC (permalink / raw)
To: Heiko Carstens
Cc: Christian Borntraeger, Janosch Frank, David Hildenbrand,
Claudio Imbrenda, kvm, linux-s390
On Thu, 15 Apr 2021 10:01:27 +0200
Heiko Carstens <hca@linux.ibm.com> wrote:
> store_regs_fmt2() has an ordering problem: first the guarded storage
> facility is enabled on the local cpu, then preemption disabled, and
> then the STGSC (store guarded storage controls) instruction is
> executed.
>
> If the process gets scheduled away between enabling the guarded
> storage facility and before preemption is disabled, this might lead to
> a special operation exception and therefore kernel crash as soon as
> the process is scheduled back and the STGSC instruction is executed.
>
> Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests")
> Cc: <stable@vger.kernel.org> # 4.12
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: s390: fix guarded storage control register handling
2021-04-15 8:01 [PATCH] KVM: s390: fix guarded storage control register handling Heiko Carstens
` (2 preceding siblings ...)
2021-04-15 9:01 ` Cornelia Huck
@ 2021-04-15 10:50 ` Christian Borntraeger
3 siblings, 0 replies; 5+ messages in thread
From: Christian Borntraeger @ 2021-04-15 10:50 UTC (permalink / raw)
To: Heiko Carstens, Janosch Frank
Cc: David Hildenbrand, Cornelia Huck, Claudio Imbrenda, kvm, linux-s390
On 15.04.21 10:01, Heiko Carstens wrote:
> store_regs_fmt2() has an ordering problem: first the guarded storage
> facility is enabled on the local cpu, then preemption disabled, and
> then the STGSC (store guarded storage controls) instruction is
> executed.
>
> If the process gets scheduled away between enabling the guarded
> storage facility and before preemption is disabled, this might lead to
> a special operation exception and therefore kernel crash as soon as
> the process is scheduled back and the STGSC instruction is executed.
>
> Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests")
> Cc: <stable@vger.kernel.org> # 4.12
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Thanks applied. Will queue for the s390kvm tree after the CI/regression has finished.
> ---
> arch/s390/kvm/kvm-s390.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 2f09e9d7dc95..24ad447e648c 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4307,16 +4307,16 @@ static void store_regs_fmt2(struct kvm_vcpu *vcpu)
> kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
> kvm_run->s.regs.diag318 = vcpu->arch.diag318_info.val;
> if (MACHINE_HAS_GS) {
> + preempt_disable();
> __ctl_set_bit(2, 4);
> if (vcpu->arch.gs_enabled)
> save_gs_cb(current->thread.gs_cb);
> - preempt_disable();
> current->thread.gs_cb = vcpu->arch.host_gscb;
> restore_gs_cb(vcpu->arch.host_gscb);
> - preempt_enable();
> if (!vcpu->arch.host_gscb)
> __ctl_clear_bit(2, 4);
> vcpu->arch.host_gscb = NULL;
> + preempt_enable();
> }
> /* SIE will save etoken directly into SDNX and therefore kvm_run */
> }
>
^ permalink raw reply [flat|nested] 5+ messages in thread