[SRU][Xenial][PATCH 2/2] UBUNTU: SAUCE: hv: don't reset hv_context.tsc_page on crash

[Joseph Salisbury]

From: Vitaly Kuznetsov <vkuznets at redhat.com>

BugLink: http://bugs.launchpad.net/bugs/1630924

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 at redhat.com>
Signed-off-by: K. Y. Srinivasan <kys at microsoft.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 56ef6718a1d8d77745033c5291e025ce18504159)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 drivers/hv/hv.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index ab1f466..60db5ff 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -317,9 +317,10 @@ 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
 }
-- 
2.7.4