linux-kernel - RE: [PATCH 2/2] x86/hyper-v: check for VP_INVAL in hyperv_flush_tlb

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Date:   Tue, 10 Jul 2018 19:41:09 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] x86/hyper-v: check for VP_INVAL in
 hyperv_flush_tlb_others()

From: Vitaly Kuznetsov <vkuznets@...hat.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().
> 
> Not checking for VP_INVAL on the first call site where we do
> 
>  if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64)
>                         goto do_ex_hypercall;
> 
> 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.
> 
> 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.
> 
> Fixes: 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI enlightenment")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/hyperv/mmu.c | 5 +++++
>  1 file changed, 5 insertions(+)

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