On Fri, 7 Aug 2020 at 17:19, Marco Elver <[email protected]> wrote: > On Fri, Aug 07, 2020 at 02:08PM +0200, Marco Elver wrote: > > On Fri, 7 Aug 2020 at 14:04, Jürgen Groß <[email protected]> wrote: > > > > > > On 07.08.20 13:38, Marco Elver wrote: > > > > On Fri, Aug 07, 2020 at 12:35PM +0200, Jürgen Groß wrote: ... > > > >> I think CONFIG_PARAVIRT_XXL shouldn't matter, but I'm not completely > > > >> sure about that. CONFIG_PARAVIRT_SPINLOCKS would be my primary suspect. > > > > > > > > Yes, PARAVIRT_XXL doesn't make a different. When disabling > > > > PARAVIRT_SPINLOCKS, however, the warnings go away. > > > > > > Thanks for testing! > > > > > > I take it you are doing the tests in a KVM guest? > > > > Yes, correct. > > > > > If so I have a gut feeling that the use of local_irq_save() and > > > local_irq_restore() in kvm_wait() might be fishy. I might be completely > > > wrong here, though. > > > > Happy to help debug more, although I might need patches or pointers > > what to play with. > > > > > BTW, I think Xen's variant of pv spinlocks is fine (no playing with IRQ > > > on/off). > > > > > > Hyper-V seems to do the same as KVM, and kicking another vcpu could be > > > problematic as well, as it is just using IPI. > > I experimented a bit more, and the below patch seems to solve the > warnings. However, that was based on your pointer about kvm_wait(), and > I can't quite tell if it is the right solution. > > My hypothesis here is simply that kvm_wait() may be called in a place > where we get the same case I mentioned to Peter, > > raw_local_irq_save(); /* or other IRQs off without tracing */ > ... > kvm_wait() /* IRQ state tracing gets confused */ > ... > raw_local_irq_restore(); > > and therefore, using raw variants in kvm_wait() works. It's also safe > because it doesn't call any other libraries that would result in corrupt > IRQ state AFAIK.
Just to follow-up, it'd still be nice to fix this. Suggestions? I could send the below as a patch, but can only go off my above hypothesis and the fact that syzbot is happier, so not entirely convincing. Thanks, -- Marco > ------ >8 ------ > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 233c77d056c9..1d412d1466f0 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -797,7 +797,7 @@ static void kvm_wait(u8 *ptr, u8 val) > if (in_nmi()) > return; > > - local_irq_save(flags); > + raw_local_irq_save(flags); > > if (READ_ONCE(*ptr) != val) > goto out; > @@ -810,10 +810,10 @@ static void kvm_wait(u8 *ptr, u8 val) > if (arch_irqs_disabled_flags(flags)) > halt(); > else > - safe_halt(); > + raw_safe_halt(); > > out: > - local_irq_restore(flags); > + raw_local_irq_restore(flags); > } > > #ifdef CONFIG_X86_32
