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KVM: PPC: Book3S HV: Drop locks before reading guest memory

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Running with CONFIG_DEBUG_ATOMIC_SLEEP reveals that HV KVM tries to
read guest memory, in order to emulate guest instructions, while
preempt is disabled and a vcore lock is held.  This occurs in
kvmppc_handle_exit_hv(), called from post_guest_process(), when
emulating guest doorbell instructions on POWER9 systems, and also
when checking whether we have hit a hypervisor breakpoint.
Reading guest memory can cause a page fault and thus cause the
task to sleep, so we need to avoid reading guest memory while
holding a spinlock or when preempt is disabled.

To fix this, we move the preempt_enable() in kvmppc_run_core() to
before the loop that calls post_guest_process() for each vcore that
has just run, and we drop and re-take the vcore lock around the calls
to kvmppc_emulate_debug_inst() and kvmppc_emulate_doorbell_instr().

Dropping the lock is safe with respect to the iteration over the
runnable vcpus in post_guest_process(); for_each_runnable_thread
is actually safe to use locklessly.  It is possible for a vcpu
to become runnable and add itself to the runnable_threads array
(code near the beginning of kvmppc_run_vcpu()) and then get included
in the iteration in post_guest_process despite the fact that it
has not just run.  This is benign because vcpu->arch.trap and
vcpu->arch.ceded will be zero.

Cc: stable@vger.kernel.org # v4.13+
Fixes: 579006944e ("KVM: PPC: Book3S HV: Virtualize doorbell facility on POWER9")
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras 2018-01-30 10:51:32 +11:00
parent 9b9b13a6d1
commit 36ee41d161
1 changed files with 12 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
arch/powerpc/kvm/book3s_hv.c
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@ -1008,8 +1008,6 @@ static int kvmppc_emulate_doorbell_instr(struct kvm_vcpu *vcpu)
struct kvm *kvm = vcpu->kvm; struct kvm *kvm = vcpu->kvm;
struct kvm_vcpu *tvcpu; struct kvm_vcpu *tvcpu;
if (!cpu_has_feature(CPU_FTR_ARCH_300))
return EMULATE_FAIL;
if (kvmppc_get_last_inst(vcpu, INST_GENERIC, &inst) != EMULATE_DONE) if (kvmppc_get_last_inst(vcpu, INST_GENERIC, &inst) != EMULATE_DONE)
return RESUME_GUEST; return RESUME_GUEST;
if (get_op(inst) != 31) if (get_op(inst) != 31)
@ -1059,6 +1057,7 @@ static int kvmppc_emulate_doorbell_instr(struct kvm_vcpu *vcpu)
return RESUME_GUEST; return RESUME_GUEST;
} }
/* Called with vcpu->arch.vcore->lock held */
static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu, static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
struct task_struct *tsk) struct task_struct *tsk)
{ {
@ -1179,7 +1178,10 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
swab32(vcpu->arch.emul_inst) : swab32(vcpu->arch.emul_inst) :
vcpu->arch.emul_inst; vcpu->arch.emul_inst;
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) { if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) {
/* Need vcore unlocked to call kvmppc_get_last_inst */
spin_unlock(&vcpu->arch.vcore->lock);
r = kvmppc_emulate_debug_inst(run, vcpu); r = kvmppc_emulate_debug_inst(run, vcpu);
spin_lock(&vcpu->arch.vcore->lock);
} else { } else {
kvmppc_core_queue_program(vcpu, SRR1_PROGILL); kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
r = RESUME_GUEST; r = RESUME_GUEST;
@ -1194,8 +1196,13 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
*/ */
case BOOK3S_INTERRUPT_H_FAC_UNAVAIL: case BOOK3S_INTERRUPT_H_FAC_UNAVAIL:
r = EMULATE_FAIL; r = EMULATE_FAIL;
if ((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) if (((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) &&
cpu_has_feature(CPU_FTR_ARCH_300)) {
/* Need vcore unlocked to call kvmppc_get_last_inst */
spin_unlock(&vcpu->arch.vcore->lock);
r = kvmppc_emulate_doorbell_instr(vcpu); r = kvmppc_emulate_doorbell_instr(vcpu);
spin_lock(&vcpu->arch.vcore->lock);
}
if (r == EMULATE_FAIL) { if (r == EMULATE_FAIL) {
kvmppc_core_queue_program(vcpu, SRR1_PROGILL); kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
r = RESUME_GUEST; r = RESUME_GUEST;
@ -2946,13 +2953,14 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
/* make sure updates to secondary vcpu structs are visible now */ /* make sure updates to secondary vcpu structs are visible now */
smp_mb(); smp_mb();
preempt_enable();
for (sub = 0; sub < core_info.n_subcores; ++sub) { for (sub = 0; sub < core_info.n_subcores; ++sub) {
pvc = core_info.vc[sub]; pvc = core_info.vc[sub];
post_guest_process(pvc, pvc == vc); post_guest_process(pvc, pvc == vc);
} }
spin_lock(&vc->lock); spin_lock(&vc->lock);
preempt_enable();
out: out:
vc->vcore_state = VCORE_INACTIVE; vc->vcore_state = VCORE_INACTIVE;