Sorry for noticing this only now, but I have been fighting with Xen PV qspinlocks last weekend:
On 02/10/2018 13:28, tip-bot for Yi Sun wrote: > Commit-ID: aaa7fc34c003bd8133a49f7634480cef6288ad55 > Gitweb: > https://git.kernel.org/tip/aaa7fc34c003bd8133a49f7634480cef6288ad55 > Author: Yi Sun <[email protected]> > AuthorDate: Thu, 27 Sep 2018 14:01:44 +0800 > Committer: Thomas Gleixner <[email protected]> > CommitDate: Tue, 2 Oct 2018 13:22:06 +0200 > > x86/hyperv: Enable PV qspinlock for Hyper-V > > Implement the necessary callbacks for PV spinlocks which allow vCPU idling > and kicking operations when running as a guest on Hyper-V > > Signed-off-by: Yi Sun <[email protected]> > Signed-off-by: Thomas Gleixner <[email protected]> > Reviewed-by: Michael Kelley <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: "K. Y. Srinivasan" <[email protected]> > Cc: Haiyang Zhang <[email protected]> > Cc: Stephen Hemminger <[email protected]> > Link: > https://lkml.kernel.org/r/[email protected] > --- > Documentation/admin-guide/kernel-parameters.txt | 5 ++ > arch/x86/hyperv/Makefile | 4 ++ > arch/x86/hyperv/hv_spinlock.c | 75 > +++++++++++++++++++++++++ > arch/x86/include/asm/mshyperv.h | 1 + > arch/x86/kernel/cpu/mshyperv.c | 14 +++++ > 5 files changed, 99 insertions(+) > ... > diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c > new file mode 100644 > index 000000000000..6d3221322d0d > --- /dev/null > +++ b/arch/x86/hyperv/hv_spinlock.c > @@ -0,0 +1,75 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +/* > + * Hyper-V specific spinlock code. > + * > + * Copyright (C) 2018, Intel, Inc. > + * > + * Author : Yi Sun <[email protected]> > + */ > + > +#define pr_fmt(fmt) "Hyper-V: " fmt > + > +#include <linux/spinlock.h> > + > +#include <asm/mshyperv.h> > +#include <asm/hyperv-tlfs.h> > +#include <asm/paravirt.h> > +#include <asm/qspinlock.h> > +#include <asm/apic.h> > + > +static bool __initdata hv_pvspin = true; > + > +static void hv_qlock_kick(int cpu) > +{ > + apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR); > +} > + > +static void hv_qlock_wait(u8 *byte, u8 val) > +{ > + unsigned long msr_val; > + > + if (READ_ONCE(*byte) != val) > + return; > + > + /* > + * Read HV_X64_MSR_GUEST_IDLE MSR can trigger the guest's > + * transition to the idle power state which can be exited > + * by an IPI even if IF flag is disabled. > + */ What if interrupts are enabled? Won't a kick happening here just interrupt and then the following rdmsr result in a hang? I believe the correct way would be to: - disable interrupts before above READ_ONCE() and restore them after the rdmsrl() - return early if in_nmi() similar as the kvm specific variant is doing it. Juergen
