linux-kernel - [PATCH] KVM: kvmclock: Fix vCPUs

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Message-Id: <1610623624-18697-1-git-send-email-wanpengli@tencent.com>
Date:   Thu, 14 Jan 2021 19:27:03 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [PATCH] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged

From: Wanpeng Li <wanpengli@...cent.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@...ux.alibaba.com>
Tested-by: Haiwei Li <lihaiwei@...cent.com>
Cc: Brijesh Singh <brijesh.singh@....com>
Cc: stable@...r.kernel.org#v4.19-rc5+
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kernel/kvmclock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index aa59374..0624290 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -296,7 +296,8 @@ static int kvmclock_setup_percpu(unsigned int cpu)
 	 * pointers. So carefully check. CPU0 has been set up in init
 	 * already.
 	 */
-	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