linux-kernel - [PATCH 4.9 110/153] hv: dont reset hv_context.tsc

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Date:   Fri, 10 Mar 2017 10:09:03 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vitaly Kuznetsov <vkuznets@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 4.9 110/153] hv: dont reset hv_context.tsc_page on crash

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vitaly Kuznetsov <vkuznets@...hat.com>

commit 56ef6718a1d8d77745033c5291e025ce18504159 upstream.

It may happen that secondary CPUs are still alive and resetting
hv_context.tsc_page will cause a consequent crash in read_hv_clock_tsc()
as we don't check for it being not NULL there. It is safe as we're not
freeing this page anyways.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/hv/hv.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -309,9 +309,10 @@ void hv_cleanup(bool crash)

 		hypercall_msr.as_uint64 = 0;
 		wrmsrl(HV_X64_MSR_REFERENCE_TSC, hypercall_msr.as_uint64);
-		if (!crash)
+		if (!crash) {
 			vfree(hv_context.tsc_page);
-		hv_context.tsc_page = NULL;
+			hv_context.tsc_page = NULL;
+		}
 	}
 #endif
 }