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Subject[PATCH v2] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged
Date
From: Wanpeng Li <wanpengli@tencent.com>

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 <zelin.deng@linux.alibaba.com>
Tested-by: Haiwei Li <lihaiwei@tencent.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: stable@vger.kernel.org#v4.19-rc5+
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
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
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