On Mon, Nov 09, 2020 at 07:19:44AM -0600, Brijesh Singh wrote:
On 9/14/20 2:00 AM, Zelin Deng wrote:
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) Cc: stable@vger.kernel.org Cc: Paolo Bonzini pbonzini@redhat.com Cc: Brijesh Singh brijesh.singh@amd.com Cc: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Zelin Deng zelin.deng@linux.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;Overall, I agree with the fix to move the kvmclock_init_mem() in the beginning of the function so that memory hvclock_mem is allocated. But curious, why do we need this check? The if (kvmclock) did not exist in original function and I don't think kvmclock_init_mem() has any dependency with it, am I missing something ?
Per my under standing if "no-kvmclock" is set in cmdline, pvclock will be disabled in guest kernel kvmclock_init() just returns without doing anything right? However in this scenarios, this function still will be executed as it is a early_initcall. To avoid a waste of memory, is it reasonable to do this check?
- 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);