Messages in this thread | | | Date | Thu, 2 Apr 2020 09:04:43 -0700 | From | Sean Christopherson <> | Subject | Re: [patch 2/2] x86/kvm/vmx: Prevent split lock detection induced #AC wreckage |
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On Thu, Apr 02, 2020 at 03:44:00PM +0000, Nadav Amit wrote: > > On Apr 2, 2020, at 8:30 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote: > > > > On Thu, Apr 02, 2020 at 02:33:00PM +0200, Thomas Gleixner wrote: > >> Without at least minimal handling for split lock detection induced #AC, VMX > >> will just run into the same problem as the VMWare hypervisor, which was > >> reported by Kenneth. > >> > >> It will inject the #AC blindly into the guest whether the guest is prepared > >> or not. > >> > >> Add the minimal required handling for it: > >> > >> - Check guest state whether CR0.AM is enabled and EFLAGS.AC is set. If > >> so, then the #AC originated from CPL3 and the guest has is prepared to > >> handle it. In this case it does not matter whether the #AC is due to a > >> split lock or a regular unaligned check. > >> > >> - Invoke a minimal split lock detection handler. If the host SLD mode is > >> sld_warn, then handle it in the same way as user space handling works: > >> Emit a warning, disable SLD and mark the current task with TIF_SLD. > >> With that resume the guest without injecting #AC. > >> > >> If the host mode is sld_fatal or sld_off, emit a warning and deliver > >> the exception to user space which can crash and burn itself. > >> > >> Mark the module with MOD_INFO(sld_safe, "Y") so the module loader does not > >> force SLD off. > > > > Some comments below. But, any objection to taking Xiaoyao's patches that > > do effectively the same things, minus the MOD_INFO()? I'll repost them in > > reply to this thread. > > IIUC they also deal with emulated split-lock accesses in the host, during > instruction emulation [1]. This seems also to be required, although I am not > sure the approach that he took once emulation encounters a split-lock is > robust.
Yep. It's "robust" in the sense that KVM won't panic the host. It's not robust from the perspective that it could possibly hose the guest. But, no sane, well-behaved guest should reach that particular emulator path on a split-lock enabled system.
> [1] https://lore.kernel.org/lkml/20200324151859.31068-5-xiaoyao.li@intel.com/
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