Re: [PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case

From: Zhenzhong Duan
Date: Wed Jul 24 2019 - 03:30:15 EST

Hi Maintainers,

Any further comments on this? Thanks


On 2019/7/3 10:23, Zhenzhong Duan wrote:
With the boot parameter "hv_nopvspin" specified a Hyperv guest should
not make use of paravirt spinlocks, but behave as if running on bare
metal. This is not true, however, as the qspinlock code will fall back
to a test-and-set scheme when it is detecting a hypervisor.

In order to avoid this disable the virt_spin_lock_key.

Same change for XEN is already in Commit e6fd28eb3522
("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: linux-hyperv@xxxxxxxxxxxxxxx
v3: remove unlikely() as suggested by Sasha

arch/x86/hyperv/hv_spinlock.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
index 07f21a0..210495b 100644
--- a/arch/x86/hyperv/hv_spinlock.c
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
void __init hv_init_spinlocks(void)
+ if (!hv_pvspin)
+ static_branch_disable(&virt_spin_lock_key);
if (!hv_pvspin || !apic ||
!(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
!(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {