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    SubjectRe: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu_idx
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    On 27.08.21 16:06, Claudio Imbrenda wrote:
    > On Fri, 27 Aug 2021 14:54:29 +0200
    > Halil Pasic <pasic@linux.ibm.com> wrote:
    >
    >> While in practice vcpu->vcpu_idx == vcpu->vcp_id is often true,
    >> it may not always be, and we must not rely on this.
    >
    > why?
    >
    > maybe add a simple explanation of why vcpu_idx and vcpu_id can be
    > different, namely:
    > KVM decides the vcpu_idx, userspace decides the vcpu_id, thus the two
    > might not match
    >
    >>
    >> Currently kvm->arch.idle_mask is indexed by vcpu_id, which implies
    >> that code like
    >> for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) {
    >> vcpu = kvm_get_vcpu(kvm, vcpu_id);
    >
    > you can also add a sentence to clarify that kvm_get_vcpu expects an
    > vcpu_idx, not an vcpu_id.
    >
    >> do_stuff(vcpu);

    I will modify the patch description accordingly before sending to Paolo.
    Thanks for noticing.


    >> }
    >> is not legit. The trouble is, we do actually use kvm->arch.idle_mask
    >> like this. To fix this problem we have two options. Either use
    >> kvm_get_vcpu_by_id(vcpu_id), which would loop to find the right vcpu_id,
    >> or switch to indexing via vcpu_idx. The latter is preferable for obvious
    >> reasons.
    >>
    >> Let us make switch from indexing kvm->arch.idle_mask by vcpu_id to
    >> indexing it by vcpu_idx. To keep gisa_int.kicked_mask indexed by the
    >> same index as idle_mask lets make the same change for it as well.
    >>
    >> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
    >> Fixes: 1ee0bc559dc3 ("KVM: s390: get rid of local_int array")
    >
    > otherwise looks good to me.
    >
    > Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    >
    >> Cc: <stable@vger.kernel.org> # 3.15+
    >> ---
    >> arch/s390/include/asm/kvm_host.h | 1 +
    >> arch/s390/kvm/interrupt.c | 12 ++++++------
    >> arch/s390/kvm/kvm-s390.c | 2 +-
    >> arch/s390/kvm/kvm-s390.h | 2 +-
    >> 4 files changed, 9 insertions(+), 8 deletions(-)
    >>
    >> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
    >> index 161a9e12bfb8..630eab0fa176 100644
    >> --- a/arch/s390/include/asm/kvm_host.h
    >> +++ b/arch/s390/include/asm/kvm_host.h
    >> @@ -957,6 +957,7 @@ struct kvm_arch{
    >> atomic64_t cmma_dirty_pages;
    >> /* subset of available cpu features enabled by user space */
    >> DECLARE_BITMAP(cpu_feat, KVM_S390_VM_CPU_FEAT_NR_BITS);
    >> + /* indexed by vcpu_idx */
    >> DECLARE_BITMAP(idle_mask, KVM_MAX_VCPUS);
    >> struct kvm_s390_gisa_interrupt gisa_int;
    >> struct kvm_s390_pv pv;
    >> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
    >> index d548d60caed2..16256e17a544 100644
    >> --- a/arch/s390/kvm/interrupt.c
    >> +++ b/arch/s390/kvm/interrupt.c
    >> @@ -419,13 +419,13 @@ static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu)
    >> static void __set_cpu_idle(struct kvm_vcpu *vcpu)
    >> {
    >> kvm_s390_set_cpuflags(vcpu, CPUSTAT_WAIT);
    >> - set_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask);
    >> + set_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask);
    >> }
    >>
    >> static void __unset_cpu_idle(struct kvm_vcpu *vcpu)
    >> {
    >> kvm_s390_clear_cpuflags(vcpu, CPUSTAT_WAIT);
    >> - clear_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask);
    >> + clear_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask);
    >> }
    >>
    >> static void __reset_intercept_indicators(struct kvm_vcpu *vcpu)
    >> @@ -3050,18 +3050,18 @@ int kvm_s390_get_irq_state(struct kvm_vcpu *vcpu, __u8 __user *buf, int len)
    >>
    >> static void __airqs_kick_single_vcpu(struct kvm *kvm, u8 deliverable_mask)
    >> {
    >> - int vcpu_id, online_vcpus = atomic_read(&kvm->online_vcpus);
    >> + int vcpu_idx, online_vcpus = atomic_read(&kvm->online_vcpus);
    >> struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
    >> struct kvm_vcpu *vcpu;
    >>
    >> - for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) {
    >> - vcpu = kvm_get_vcpu(kvm, vcpu_id);
    >> + for_each_set_bit(vcpu_idx, kvm->arch.idle_mask, online_vcpus) {
    >> + vcpu = kvm_get_vcpu(kvm, vcpu_idx);
    >> if (psw_ioint_disabled(vcpu))
    >> continue;
    >> deliverable_mask &= (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
    >> if (deliverable_mask) {
    >> /* lately kicked but not yet running */
    >> - if (test_and_set_bit(vcpu_id, gi->kicked_mask))
    >> + if (test_and_set_bit(vcpu_idx, gi->kicked_mask))
    >> return;
    >> kvm_s390_vcpu_wakeup(vcpu);
    >> return;
    >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
    >> index 4527ac7b5961..8580543c5bc3 100644
    >> --- a/arch/s390/kvm/kvm-s390.c
    >> +++ b/arch/s390/kvm/kvm-s390.c
    >> @@ -4044,7 +4044,7 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu)
    >> kvm_s390_patch_guest_per_regs(vcpu);
    >> }
    >>
    >> - clear_bit(vcpu->vcpu_id, vcpu->kvm->arch.gisa_int.kicked_mask);
    >> + clear_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.gisa_int.kicked_mask);
    >>
    >> vcpu->arch.sie_block->icptcode = 0;
    >> cpuflags = atomic_read(&vcpu->arch.sie_block->cpuflags);
    >> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
    >> index 9fad25109b0d..ecd741ee3276 100644
    >> --- a/arch/s390/kvm/kvm-s390.h
    >> +++ b/arch/s390/kvm/kvm-s390.h
    >> @@ -79,7 +79,7 @@ static inline int is_vcpu_stopped(struct kvm_vcpu *vcpu)
    >>
    >> static inline int is_vcpu_idle(struct kvm_vcpu *vcpu)
    >> {
    >> - return test_bit(vcpu->vcpu_id, vcpu->kvm->arch.idle_mask);
    >> + return test_bit(kvm_vcpu_get_idx(vcpu), vcpu->kvm->arch.idle_mask);
    >> }
    >>
    >> static inline int kvm_is_ucontrol(struct kvm *kvm)
    >>
    >> base-commit: 77dd11439b86e3f7990e4c0c9e0b67dca82750ba
    >

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