linux-kernel - [PATCH] KVM: x86: kvmclock_init_mem() should be called any way

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Date:   Mon, 17 Aug 2020 13:57:39 +0800
From:   Zelin Deng <zelin.deng@...ux.alibaba.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Brijesh Singh <brijesh.singh@....com>,
        Artie Ding <artie.ding@...ux.alibaba.com>,
        Caspar Zhang <caspar@...ux.alibaba.com>,
        Zelin Deng <zelin.deng@...ux.alibaba.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86: kvmclock_init_mem() should be called any way

pvclock data pointers of vCPUs >= HVC_BOOT_ARRAY_SIZE (64) are stored in
hvclock_mem wihch is initialized in kvmclock_init_mem().
Here're 3 scenarios in current implementation:
    - no-kvmclock is set in cmdline. kvm pv clock driver is disabled,
      no impact.
    - no-kvmclock-vsyscall is set in cmdline. kvmclock_init_mem() won't
      be called. No memory for storing pvclock data of vCPUs >= 64, vCPUs
      >= 64 can not be online or hotpluged.
    - tsc unstable. kvmclock_init_mem() won't be called. vCPUs >= 64 can
      not be online or hotpluged.
It's not reasonable that vCPUs hotplug have been impacted by last 2
scenarios. Hence move kvmclock_init_mem() to front, in case hvclock_mem
can not be initialized unexpectedly.

Fixes: 6a1cac56f41f9 (x86/kvm: Use __bss_decrypted attribute in shared variables)
Signed-off-by: Zelin Deng <zelin.deng@...ux.alibaba.com>
---
 arch/x86/kernel/kvmclock.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 34b18f6eeb2c..1abbda25e037 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -271,7 +271,14 @@ static int __init kvm_setup_vsyscall_timeinfo(void)
 {
 #ifdef CONFIG_X86_64
 	u8 flags;
+#endif
+
+	if (!kvmclock)
+		return 0;
+
+	kvmclock_init_mem();
 
+#ifdef CONFIG_X86_64
 	if (!per_cpu(hv_clock_per_cpu, 0) || !kvmclock_vsyscall)
 		return 0;
 
@@ -282,8 +289,6 @@ static int __init kvm_setup_vsyscall_timeinfo(void)
 	kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
 #endif
 
-	kvmclock_init_mem();
-
 	return 0;
 }
 early_initcall(kvm_setup_vsyscall_timeinfo);
-- 
2.20.1