On Tue, Aug 04, 2026 at 07:15:41AM +0000, Dmitry Ilvokhin wrote:
> From: Peter Zijlstra <[email protected]>
>
> queued_spin_lock_slowpath() and queued_spin_unlock() are dispatched
> through pv_ops_lock via the paravirt-ops ALTERNATIVE machinery, which
> picks the target (native inline store / hypervisor call) once at boot
> and cannot change at runtime.
>
> Convert both to static_call(). The site becomes a direct call patched in
> place (one byte smaller), and on native the unlock still collapses to
> the inline "movb $0, (%rdi)" store, so the fast path is unchanged.
>
> Unlike the ALTERNATIVE mechanism, a static_call() target can also be
> updated at runtime via static_call_update(). This is a prerequisite for
> the contended_release tracepoint, which has to swap in a traced unlock
> while the system is running.
>
> [ ilvokhin: commit message; fix PARAVIRT_SPINLOCKS=n build; teach
> __static_call_validate() about the inline unlock insn; make the
> slowpath site module-safe: static_call_mod() +
> EXPORT_STATIC_CALL_TRAMP(); pass @lock to the callee-save unlock,
> fixing a boot hang under CALL_DEPTH_TRACKING. Boot tested native + KVM
> PV guest. ]
>
> Link:
> https://lore.kernel.org/all/[email protected]/
> Co-developed-by: Dmitry Ilvokhin <[email protected]>
> Signed-off-by: Dmitry Ilvokhin <[email protected]>
This needs Peter's SOB.
> ---
> arch/x86/hyperv/hv_spinlock.c | 4 ++--
> arch/x86/include/asm/cpufeatures.h | 1 -
> arch/x86/include/asm/paravirt-spinlock.h | 19 +++++++++++------
> arch/x86/kernel/kvm.c | 5 ++---
> arch/x86/kernel/paravirt-spinlocks.c | 12 +++++------
> arch/x86/kernel/static_call.c | 27 ++++++++++++++++++++++++
> arch/x86/xen/spinlock.c | 5 ++---
> tools/arch/x86/include/asm/cpufeatures.h | 1 -
> 8 files changed, 51 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
> index 210b494e4de0..6b4bdea18218 100644
> --- a/arch/x86/hyperv/hv_spinlock.c
> +++ b/arch/x86/hyperv/hv_spinlock.c
> @@ -78,8 +78,8 @@ void __init hv_init_spinlocks(void)
> pr_info("PV spinlocks enabled\n");
>
> __pv_init_lock_hash();
> - pv_ops_lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
> - pv_ops_lock.queued_spin_unlock =
> PV_CALLEE_SAVE(__pv_queued_spin_unlock);
> + static_call_update(queued_spin_lock_slowpath,
> __pv_queued_spin_lock_slowpath);
> + static_call_update(queued_spin_unlock,
> __raw_callee_save___pv_queued_spin_unlock);
> pv_ops_lock.wait = hv_qlock_wait;
> pv_ops_lock.kick = hv_qlock_kick;
> pv_ops_lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
> diff --git a/arch/x86/include/asm/cpufeatures.h
> b/arch/x86/include/asm/cpufeatures.h
> index 1b4a48bff18f..e41fe5c24841 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -225,7 +225,6 @@
> #define X86_FEATURE_EPT_AD ( 8*32+17) /* "ept_ad" Intel Extended
> Page Table access-dirty bit */
> #define X86_FEATURE_VMCALL ( 8*32+18) /* Hypervisor supports the
> VMCALL instruction */
> #define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* VMware prefers
> VMMCALL hypercall instruction */
> -#define X86_FEATURE_PVUNLOCK ( 8*32+20) /* PV unlock function */
No, do:
/* free: was #define X86_FEATURE_PVUNLOCK ( 8*32+20) /* PV unlock
function */
so that we can reuse it by finding it easier.
> #define X86_FEATURE_VCPUPREEMPT ( 8*32+21) /* PV
> vcpu_is_preempted function */
> #define X86_FEATURE_TDX_GUEST ( 8*32+22) /* "tdx_guest" Intel
> Trust Domain Extensions Guest */
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
