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Message-ID: <20190305123329.GK32477@hirez.programming.kicks-ass.net>
Date: Tue, 5 Mar 2019 13:33:29 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kairui Song <kasong@...hat.com>
Cc: linux-kernel@...r.kernel.org,
"K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Sasha Levin <sashal@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Dave Young <dyoung@...hat.com>, x86@...nel.org,
devel@...uxdriverproject.org
Subject: Re: [PATCH v2] x86, hyperv: fix kernel panic when kexec on HyperV
On Tue, Mar 05, 2019 at 08:17:03PM +0800, Kairui Song wrote:
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 7abb09e2eeb8..34aa1e953dfc 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -406,6 +406,12 @@ void hyperv_cleanup(void)
> /* Reset our OS id */
> wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
>
> + /* Cleanup hypercall page reference before reset the page */
> + hv_hypercall_pg = NULL;
> +
> + /* Make sure page reference is cleared before wrmsr */
This comment forgets to tell us who cares about this. And why the wrmsr
itself isn't serializing enough.
> + wmb();
> +
> /* Reset the hypercall page */
> hypercall_msr.as_uint64 = 0;
> wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
That looks like a fake MSR; and you're telling me that VMEXIT doesn't
serialize?
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