On Thu, Apr 16, 2020 at 11:29:59PM -0700, Dexuan Cui wrote: > Unlike the other CPUs, CPU0 is never offlined during hibernation. So in the > resume path, the "new" kernel's VP assist page is not suspended (i.e. > disabled), and later when we jump to the "old" kernel, the page is not > properly re-enabled for CPU0 with the allocated page from the old kernel. > > So far, the VP assist page is only used by hv_apic_eoi_write(). When the > page is not properly re-enabled, hvp->apic_assist is always 0, so the > HV_X64_MSR_EOI MSR is always written. This is not ideal with respect to > performance, but Hyper-V can still correctly handle this. > > The issue is: the hypervisor can corrupt the old kernel memory, and hence > sometimes cause unexpected behaviors, e.g. when the old kernel's non-boot > CPUs are being onlined in the resume path, the VM can hang or be killed > due to virtual triple fault. > > Fix the issue by calling hv_cpu_die()/hv_cpu_init() in the syscore ops. > > Without the fix, hibernation can fail at a rate of 1/300 ~ 1/500. > With the fix, hibernation can pass a long-haul test of 2000 rounds. > > Fixes: 05bd330a7fd8 ("x86/hyperv: Suspend/resume the hypercall page for hibernation") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > --- > arch/x86/hyperv/hv_init.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > index b0da5320bcff..4d3ce86331a3 100644 > --- a/arch/x86/hyperv/hv_init.c > +++ b/arch/x86/hyperv/hv_init.c > @@ -72,7 +72,8 @@ static int hv_cpu_init(unsigned int cpu) > struct page *pg; > > input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg); > - pg = alloc_page(GFP_KERNEL); > + /* hv_cpu_init() can be called with IRQs disabled from hv_resume() */ > + pg = alloc_page(GFP_ATOMIC); IMHO it would be better to only tap into the reserve pool if so required, e.g. pg = alloc_page(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL); Wei.