From: Wanpeng Li <redacted>

The per-cpu vsyscall pvclock data pointer assigns either an element of the
static array hv_clock_boot (#vCPU <= 64) or dynamically allocated memory
hvclock_mem (vCPU > 64), the dynamically memory will not be allocated if
kvmclock vsyscall is disabled, this can result in cpu hotpluged fails in
kvmclock_setup_percpu() which returns -ENOMEM. This patch fixes it by not
assigning vsyscall pvclock data pointer if kvmclock vdso_clock_mode is not
VDSO_CLOCKMODE_PVCLOCK.

Fixes: 6a1cac56f4 ("x86/kvm: Use __bss_decrypted attribute in shared variables")
Reported-by: Zelin Deng <redacted>
Tested-by: Haiwei Li <redacted>
Cc: Brijesh Singh <redacted>
Cc: stable@vger.kernel.org#v4.19-rc5+
Signed-off-by: Wanpeng Li <redacted>
---
v1 -> v2:
 * add code comments

 arch/x86/kernel/kvmclock.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index aa59374..01d4e55c 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c

@@ -294,9 +294,11 @@ static int kvmclock_setup_percpu(unsigned int cpu)
        /*
         * The per cpu area setup replicates CPU0 data to all cpu
         * pointers. So carefully check. CPU0 has been set up in init
-        * already.
+        * already. Assign vsyscall pvclock data pointer iff kvmclock
+        * vsyscall is enabled.
         */
-       if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
+       if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)) ||
+           (kvm_clock.vdso_clock_mode != VDSO_CLOCKMODE_PVCLOCK))
                return 0;

        /* Use the static page for the first CPUs, allocate otherwise */
--

2.7.4