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Date: Tue, 21 Apr 2020 10:07:23 +0100 From: Wei Liu <wei.liu@...nel.org> To: Dexuan Cui <decui@...rosoft.com> Cc: bp@...en8.de, haiyangz@...rosoft.com, hpa@...or.com, kys@...rosoft.com, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...hat.com, sthemmin@...rosoft.com, tglx@...utronix.de, x86@...nel.org, mikelley@...rosoft.com, vkuznets@...hat.com, wei.liu@...nel.org, stable@...r.kernel.org Subject: Re: [PATCH v2] x86/hyperv: Suspend/resume the VP assist page for hibernation On Mon, Apr 20, 2020 at 07:46:11PM -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. not > 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 used by hv_apic_eoi_write(), and is also > used in the case of nested virtualization (running KVM atop Hyper-V). > > For 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 according to the Hyper-V spec; nevertheless, Linux > still must update the Hyper-V hypervisor with the correct VP assist page > to prevent Hyper-V from writing to the stale page, which causes guest > memory corruption and consequently may have caused the hangs and triple > faults seen during non-boot CPUs resume. > > 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 runs. > > In the case of nested virtualization, disabling/reenabling the assist > page upon hibernation may be unsafe if there are active L2 guests. > It looks KVM should be enhanced to abort the hibernation request if > there is any active L2 guest. > > Fixes: 05bd330a7fd8 ("x86/hyperv: Suspend/resume the hypercall page for hibernation") > Cc: stable@...r.kernel.org > Signed-off-by: Dexuan Cui <decui@...rosoft.com> Applied to hyperv-fixes. Thanks.
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