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From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        "x86@kernel.org" <x86@kernel.org>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 2/2] x86/hyper-v: check for VP_INVAL in
 hyperv_flush_tlb_others()
Thread-Topic: [PATCH 2/2] x86/hyper-v: check for VP_INVAL in
 hyperv_flush_tlb_others()
Thread-Index: AQHUF6vplaCzQub/mU22elwWHEbh1aSI3EUA
Date:   Tue, 10 Jul 2018 19:41:09 +0000
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 <20180709174012.17429-3-vkuznets@redhat.com>
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From: Vitaly Kuznetsov <vkuznets@redhat.com>  Monday, July 9, 2018 10:40 AM
> Commit 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI
>  enlightenment") pre-filled hv_vp_index with VP_INVAL so it is now
> (theoretically) possible to observe hv_cpu_number_to_vp_number()
> returning VP_INVAL. We need to check for that in hyperv_flush_tlb_others(=
).
>=20
> Not checking for VP_INVAL on the first call site where we do
>=20
>  if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >=3D 64)
>                         goto do_ex_hypercall;
>=20
> is OK, in case we're eligible for non-ex hypercall we'll catch the
> issue later in for_each_cpu() cycle and in case we'll be doing ex-
> hypercall cpumask_to_vpset() will fail.
>=20
> It would be nice to change hv_cpu_number_to_vp_number() return
> value's type to 'u32' but this will likely be a bigger change as
> all call sites need to be checked first.
>=20
> Fixes: 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI enl=
ightenment")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/hyperv/mmu.c | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Michael Kelley <mikelley@microsoft.com>