linux-kernel - Re: [PATCH 1/1] X86/Hyper-V:: Fix the circular dependency in IPI enlightenment.

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Message-ID: <20180705222302.GB5410@gmail.com>
Date:   Fri, 6 Jul 2018 00:23:02 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     KY Srinivasan <kys@...rosoft.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>
Subject: Re: [PATCH 1/1] X86/Hyper-V:: Fix the circular dependency in IPI
 enlightenment.


* KY Srinivasan <kys@...rosoft.com> wrote:

> 
> 
> > -----Original Message-----
> > From: Ingo Molnar <mingo.kernel.org@...il.com> On Behalf Of Ingo Molnar
> > Sent: Thursday, July 5, 2018 8:38 AM
> > To: KY Srinivasan <kys@...rosoft.com>
> > Cc: x86@...nel.org; gregkh@...uxfoundation.org; linux-
> > kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> > apw@...onical.com; jasowang@...hat.com; tglx@...utronix.de;
> > hpa@...or.com; Stephen Hemminger <sthemmin@...rosoft.com>; Michael
> > Kelley (EOSG) <Michael.H.Kelley@...rosoft.com>; vkuznets@...hat.com
> > Subject: Re: [PATCH 1/1] X86/Hyper-V:: Fix the circular dependency in IPI
> > enlightenment.
> > 
> > 
> > * KY Srinivasan <kys@...rosoft.com> wrote:
> > 
> > >
> > >
> > > > -----Original Message-----
> > > > From: Ingo Molnar <mingo.kernel.org@...il.com> On Behalf Of Ingo
> > Molnar
> > > > Sent: Wednesday, July 4, 2018 9:11 AM
> > > > To: KY Srinivasan <kys@...rosoft.com>
> > > > Cc: x86@...nel.org; gregkh@...uxfoundation.org; linux-
> > > > kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> > > > apw@...onical.com; jasowang@...hat.com; tglx@...utronix.de;
> > > > hpa@...or.com; Stephen Hemminger <sthemmin@...rosoft.com>;
> > Michael
> > > > Kelley (EOSG) <Michael.H.Kelley@...rosoft.com>;
> > vkuznets@...hat.com
> > > > Subject: Re: [PATCH 1/1] X86/Hyper-V:: Fix the circular dependency in IPI
> > > > enlightenment.
> > > >
> > > >
> > > > * kys@...uxonhyperv.com <kys@...uxonhyperv.com> wrote:
> > > >
> > > > > From: "K. Y. Srinivasan" <kys@...rosoft.com>
> > > > >
> > > > > The IPI hypercalls depend on being able to map the Linux notion of CPU
> > ID
> > > > > to the hypervisor's notion of the CPU ID. The array hv_vp_index[]
> > provides
> > > > > this mapping. Code for populating this array depends on the IPI
> > > > functionality.
> > > > > Break this circular dependency.
> > > > >
> > > > > Fixes: 68bb7bfb7985 ("X86/Hyper-V: Enable IPI enlightenments")
> > > > >
> > > > > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > > > > Tested-by: Michael Kelley <mikelley@...rosoft.com>
> > > > > ---
> > > > >  arch/x86/hyperv/hv_apic.c       | 5 +++++
> > > > >  arch/x86/hyperv/hv_init.c       | 5 ++++-
> > > > >  arch/x86/include/asm/mshyperv.h | 2 ++
> > > > >  3 files changed, 11 insertions(+), 1 deletion(-)
> > > >
> > > > Ugh, this patch wasn't even build tested, on 64-bit allyes/allmodconfig:
> > > >
> > > >  arch/x86/hyperv/hv_apic.c: In function ‘__send_ipi_mask’:
> > > >  arch/x86/hyperv/hv_apic.c:171:4: error: label ‘ipi_mask_done’ used but
> > not
> > > > defined
> > > >  scripts/Makefile.build:317: recipe for target 'arch/x86/hyperv/hv_apic.o'
> > > > failed
> > > >  make[2]: *** [arch/x86/hyperv/hv_apic.o] Error 1
> > >
> > > Sorry Ingo. I had a clean build on the linux-next tree (tag: next-20180702)
> > that
> > > I used to base this patch. What was the tree you applied the patch to?
> > 
> > If you look at the error message, it won't build against *any* tree, because
> > there's no 'ipi_mask_done' label either in the kernel source, or introduced
> > by the patch.
> > 
> > So whatever tree you used it on, if you build arch/x86/hyperv/hv_apic.o it
> > should
> > be broken.
> 
> Ingo,
> 
> I am confused. The label ipi_mask_done was introduced in this patch
> (the patch under question fixes a circular dependency in this patch):
> 
> commit 68bb7bfb7985df2bd15c2dc975cb68b7a901488a
> Author: K. Y. Srinivasan <kys@...rosoft.com>
> Date:   Wed May 16 14:53:31 2018 -0700
> 
>     X86/Hyper-V: Enable IPI enlightenments
> 
>     Hyper-V supports hypercalls to implement IPI; use them.
> 
>     Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
>     Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>     Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> 
> This patch was committed by Thomas some weeks ago and is in linux-next.
> This patch is also in 4.18-rc3.

And then that name was changed to a different label in:

  4bd06060762b: x86/hyper-v: Use cheaper HVCALL_SEND_IPI hypercall when possible

So maybe you were testing on an older kernel. Could you try the latest -tip?

Thanks,

	Ingo