Message ID | 20230217102926.84817-2-roxana.nicolescu@canonical.com |
---|---|
State | New |
Headers | show |
Series | KVM: s390: pv: don't allow userspace to set the clock under PV | expand |
On 17.02.23 11:29, Roxana Nicolescu wrote: > From: Claudio Imbrenda <imbrenda@linux.ibm.com> > > BugLink: https://bugs.launchpad.net/bugs/1999882 > > [ Upstream commit c0573ba5c5a2244dc02060b1f374d4593c1d20b7 ] > > When handling the SCK instruction, the kvm lock is taken, even though > the vcpu lock is already being held. The normal locking order is kvm > lock first and then vcpu lock. This is can (and in some circumstances > does) lead to deadlocks. > > The function kvm_s390_set_tod_clock is called both by the SCK handler > and by some IOCTLs to set the clock. The IOCTLs will not hold the vcpu > lock, so they can safely take the kvm lock. The SCK handler holds the > vcpu lock, but will also somehow need to acquire the kvm lock without > relinquishing the vcpu lock. > > The solution is to factor out the code to set the clock, and provide > two wrappers. One is called like the original function and does the > locking, the other is called kvm_s390_try_set_tod_clock and uses > trylock to try to acquire the kvm lock. This new wrapper is then used > in the SCK handler. If locking fails, -EAGAIN is returned, which is > eventually propagated to userspace, thus also freeing the vcpu lock and > allowing for forward progress. > > This is not the most efficient or elegant way to solve this issue, but > the SCK instruction is deprecated and its performance is not critical. > > The goal of this patch is just to provide a simple but correct way to > fix the bug. > > Fixes: 6a3f95a6b04c ("KVM: s390: Intercept SCK instruction") > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com> > Reviewed-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> > Link: https://lore.kernel.org/r/20220301143340.111129-1-imbrenda@linux.ibm.com > Cc: stable@vger.kernel.org > Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com> > Stable-dep-of: 6973091d1b50 ("KVM: s390: pv: don't allow userspace to set the clock under PV") > Signed-off-by: Sasha Levin <sashal@kernel.org> > (backported from commit c0573ba5c5a2244dc02060b1f374d4593c1d20b7) > [roxanan: no adjustments needed] That is a (cherry picked from c0573ba5c5a2244dc02060b1f374d4593c1d20b7) To be replaced when applying. > Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com> > --- > arch/s390/kvm/kvm-s390.c | 19 ++++++++++++++++--- > arch/s390/kvm/kvm-s390.h | 4 ++-- > arch/s390/kvm/priv.c | 15 ++++++++++++++- > 3 files changed, 32 insertions(+), 6 deletions(-) > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 1fb8b8a9fa0f..0f1b0dde0de3 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -3940,14 +3940,12 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu) > return 0; > } > > -void kvm_s390_set_tod_clock(struct kvm *kvm, > - const struct kvm_s390_vm_tod_clock *gtod) > +static void __kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) > { > struct kvm_vcpu *vcpu; > struct kvm_s390_tod_clock_ext htod; > int i; > > - mutex_lock(&kvm->lock); > preempt_disable(); > > get_tod_clock_ext((char *)&htod); > @@ -3968,7 +3966,22 @@ void kvm_s390_set_tod_clock(struct kvm *kvm, > > kvm_s390_vcpu_unblock_all(kvm); > preempt_enable(); > +} > + > +void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) > +{ > + mutex_lock(&kvm->lock); > + __kvm_s390_set_tod_clock(kvm, gtod); > + mutex_unlock(&kvm->lock); > +} > + > +int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) > +{ > + if (!mutex_trylock(&kvm->lock)) > + return 0; > + __kvm_s390_set_tod_clock(kvm, gtod); > mutex_unlock(&kvm->lock); > + return 1; > } > > /** > diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h > index 817d213693e0..c94c1e29eeca 100644 > --- a/arch/s390/kvm/kvm-s390.h > +++ b/arch/s390/kvm/kvm-s390.h > @@ -335,8 +335,8 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu); > int kvm_s390_handle_sigp_pei(struct kvm_vcpu *vcpu); > > /* implemented in kvm-s390.c */ > -void kvm_s390_set_tod_clock(struct kvm *kvm, > - const struct kvm_s390_vm_tod_clock *gtod); > +void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod); > +int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod); > long kvm_arch_fault_in_page(struct kvm_vcpu *vcpu, gpa_t gpa, int writable); > int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long addr); > int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr); > diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c > index 840b383ba756..8f03992d25cc 100644 > --- a/arch/s390/kvm/priv.c > +++ b/arch/s390/kvm/priv.c > @@ -103,7 +103,20 @@ static int handle_set_clock(struct kvm_vcpu *vcpu) > return kvm_s390_inject_prog_cond(vcpu, rc); > > VCPU_EVENT(vcpu, 3, "SCK: setting guest TOD to 0x%llx", gtod.tod); > - kvm_s390_set_tod_clock(vcpu->kvm, >od); > + /* > + * To set the TOD clock the kvm lock must be taken, but the vcpu lock > + * is already held in handle_set_clock. The usual lock order is the > + * opposite. As SCK is deprecated and should not be used in several > + * cases, for example when the multiple epoch facility or TOD clock > + * steering facility is installed (see Principles of Operation), a > + * slow path can be used. If the lock can not be taken via try_lock, > + * the instruction will be retried via -EAGAIN at a later point in > + * time. > + */ > + if (!kvm_s390_try_set_tod_clock(vcpu->kvm, >od)) { > + kvm_s390_retry_instr(vcpu); > + return -EAGAIN; > + } > > kvm_s390_set_psw_cc(vcpu, 0); > return 0;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 1fb8b8a9fa0f..0f1b0dde0de3 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3940,14 +3940,12 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu) return 0; } -void kvm_s390_set_tod_clock(struct kvm *kvm, - const struct kvm_s390_vm_tod_clock *gtod) +static void __kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) { struct kvm_vcpu *vcpu; struct kvm_s390_tod_clock_ext htod; int i; - mutex_lock(&kvm->lock); preempt_disable(); get_tod_clock_ext((char *)&htod); @@ -3968,7 +3966,22 @@ void kvm_s390_set_tod_clock(struct kvm *kvm, kvm_s390_vcpu_unblock_all(kvm); preempt_enable(); +} + +void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) +{ + mutex_lock(&kvm->lock); + __kvm_s390_set_tod_clock(kvm, gtod); + mutex_unlock(&kvm->lock); +} + +int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod) +{ + if (!mutex_trylock(&kvm->lock)) + return 0; + __kvm_s390_set_tod_clock(kvm, gtod); mutex_unlock(&kvm->lock); + return 1; } /** diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h index 817d213693e0..c94c1e29eeca 100644 --- a/arch/s390/kvm/kvm-s390.h +++ b/arch/s390/kvm/kvm-s390.h @@ -335,8 +335,8 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu); int kvm_s390_handle_sigp_pei(struct kvm_vcpu *vcpu); /* implemented in kvm-s390.c */ -void kvm_s390_set_tod_clock(struct kvm *kvm, - const struct kvm_s390_vm_tod_clock *gtod); +void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod); +int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod); long kvm_arch_fault_in_page(struct kvm_vcpu *vcpu, gpa_t gpa, int writable); int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long addr); int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr); diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c index 840b383ba756..8f03992d25cc 100644 --- a/arch/s390/kvm/priv.c +++ b/arch/s390/kvm/priv.c @@ -103,7 +103,20 @@ static int handle_set_clock(struct kvm_vcpu *vcpu) return kvm_s390_inject_prog_cond(vcpu, rc); VCPU_EVENT(vcpu, 3, "SCK: setting guest TOD to 0x%llx", gtod.tod); - kvm_s390_set_tod_clock(vcpu->kvm, >od); + /* + * To set the TOD clock the kvm lock must be taken, but the vcpu lock + * is already held in handle_set_clock. The usual lock order is the + * opposite. As SCK is deprecated and should not be used in several + * cases, for example when the multiple epoch facility or TOD clock + * steering facility is installed (see Principles of Operation), a + * slow path can be used. If the lock can not be taken via try_lock, + * the instruction will be retried via -EAGAIN at a later point in + * time. + */ + if (!kvm_s390_try_set_tod_clock(vcpu->kvm, >od)) { + kvm_s390_retry_instr(vcpu); + return -EAGAIN; + } kvm_s390_set_psw_cc(vcpu, 0); return 0;