On Mon, Sep 30, 2019 at 08:44:36PM +0800, Zhenzhong Duan wrote: > There are cases where a guest tries to switch spinlocks to bare metal > behavior (e.g. by setting "xen_nopvspin" on XEN platform and > "hv_nopvspin" on HYPER_V). > > That feature is missed on KVM, add a new parameter "nopvspin" to disable > PV spinlocks for KVM guest. > > This new parameter is also used to replace "xen_nopvspin" and > "hv_nopvspin".
This is confusing as there are no Xen or Hyper-V changes in this patch. Please make it clear that you're talking about future patches, e.g.: The new 'nopvspin' parameter will also replace Xen and Hyper-V specific parameters in future patches. > > The global variable pvspin isn't defined as __initdata as it's used at > runtime by XEN guest. Same comment as above regarding what this patch is doing versus what will be done in the future. Arguably you should even mark it __initdata in this patch and deal with conflict in the Xen patch, e.g. use it only to set the existing xen_pvspin variable. > Signed-off-by: Zhenzhong Duan <[email protected]> > Cc: Jonathan Corbet <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krcmar <[email protected]> > Cc: Sean Christopherson <[email protected]> > Cc: Vitaly Kuznetsov <[email protected]> > Cc: Wanpeng Li <[email protected]> > Cc: Jim Mattson <[email protected]> > Cc: Joerg Roedel <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Will Deacon <[email protected]> > --- > Documentation/admin-guide/kernel-parameters.txt | 4 ++++ > arch/x86/include/asm/qspinlock.h | 1 + > arch/x86/kernel/kvm.c | 7 +++++++ > kernel/locking/qspinlock.c | 7 +++++++ > 4 files changed, 19 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > b/Documentation/admin-guide/kernel-parameters.txt > index c7ac2f3..4b956d8 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5330,6 +5330,10 @@ > as generic guest with no PV drivers. Currently support > XEN HVM, KVM, HYPER_V and VMWARE guest. > > + nopvspin [X86,KVM] Disables the qspinlock slow path > + using PV optimizations which allow the hypervisor to > + 'idle' the guest on lock contention. > + > xirc2ps_cs= [NET,PCMCIA] > Format: > > <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] > diff --git a/arch/x86/include/asm/qspinlock.h > b/arch/x86/include/asm/qspinlock.h > index 444d6fd..34a4484 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -32,6 +32,7 @@ static __always_inline u32 > queued_fetch_set_pending_acquire(struct qspinlock *lo > extern void __pv_init_lock_hash(void); > extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock > *lock); > +extern bool pvspin; > > #define queued_spin_unlock queued_spin_unlock > /** > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index e820568..a4f108d 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -842,6 +842,13 @@ void __init kvm_spinlock_init(void) > if (num_possible_cpus() == 1) > return; > > + if (!pvspin) { > + pr_info("PV spinlocks disabled\n"); > + static_branch_disable(&virt_spin_lock_key); > + return; > + } > + pr_info("PV spinlocks enabled\n"); These prints could be confusing as KVM also disables PV spinlocks when it sees KVM_HINTS_REALTIME. > + > __pv_init_lock_hash(); > pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; > pv_ops.lock.queued_spin_unlock = > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 2473f10..945b510 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, > u32 val) > #include "qspinlock_paravirt.h" > #include "qspinlock.c" > > +bool pvspin = true; This can be __ro_after_init, or probably better __initdata and have Xen snapshot the value for its use case. Personal preference: I'd invert the bool and name it nopvspin to make it easier to connect the variable to the kernel param. > +static __init int parse_nopvspin(char *arg) > +{ > + pvspin = false; > + return 0; > +} > +early_param("nopvspin", parse_nopvspin); > #endif > -- > 1.8.3.1 >
