From: Peter Zijlstra <peterz@infradead.org>
To: Kairui Song <kasong@redhat.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Sasha Levin <sashal@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Dave Young <dyoung@redhat.com>,
the arch/x86 maintainers <x86@kernel.org>,
devel@linuxdriverproject.org
Subject: Re: [RFC PATCH] x86, hyperv: fix kernel panic when kexec on HyperV VM
Date: Tue, 5 Mar 2019 13:28:27 +0100 [thread overview]
Message-ID: <20190305122827.GJ32477@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CACPcB9c86eT=kXcXkBkUjZnifk5bZ71SogfW2tyNudrVmWbnDQ@mail.gmail.com>
On Wed, Feb 27, 2019 at 10:55:46PM +0800, Kairui Song wrote:
> On Wed, Feb 27, 2019 at 8:02 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Tue, Feb 26, 2019 at 11:56:15PM +0800, Kairui Song wrote:
> > > arch/x86/hyperv/hv_init.c | 4 ++++
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > > index 7abb09e2eeb8..92291c18d716 100644
> > > --- a/arch/x86/hyperv/hv_init.c
> > > +++ b/arch/x86/hyperv/hv_init.c
> > > @@ -406,6 +406,10 @@ void hyperv_cleanup(void)
> > > /* Reset our OS id */
> > > wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
> > >
> > > + /* Cleanup page reference before reset the page */
> > > + hv_hypercall_pg = NULL;
> > > + wmb();
> >
> > What do we need that SFENCE for? Any why does it lack a comment?
>
> Hi, that's for ensuring the hv_hypercall_pg is reset to NULL before
> the following wrmsr call. The wrmsr call will make the pointer address
> invalid.
WRMSR is a serializing instruction (except for TSC_DEADLINE and the
X2APIC).
> I can add some comment in V2 if this is OK.
Barriers must always have a comment.
next prev parent reply other threads:[~2019-03-05 12:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-26 15:56 Kairui Song
2019-02-26 16:39 ` Vitaly Kuznetsov
2019-02-27 12:01 ` Peter Zijlstra
2019-02-27 14:55 ` Kairui Song
2019-03-05 12:28 ` Peter Zijlstra [this message]
2019-03-05 13:32 ` Kairui Song
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