Messages in this thread Patch in this message | | | Subject | Re: [PATCH v6 2/4] KVM: x86: report negative values from wrmsr emulation to userspace | From | Qian Cai <> | Date | Tue, 27 Oct 2020 16:31:26 -0400 |
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On Mon, 2020-10-26 at 15:40 -0400, Qian Cai wrote: > On Wed, 2020-09-23 at 00:10 +0300, Maxim Levitsky wrote: > > This will allow the KVM to report such errors (e.g -ENOMEM) > > to the userspace. > > > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> > > Reverting this and its dependency: > > 72f211ecaa80 KVM: x86: allow kvm_x86_ops.set_efer to return an error value > > on the top of linux-next (they have also unfortunately merged into the > mainline > at the same time) fixed an issue that a simple Intel KVM guest is unable to > boot > below.
So I debug this a bit more. This also breaks nested virt (VMX). We have here:
[ 345.504403] kvm [1491]: vcpu0 unhandled rdmsr: 0x4e data 0x0 [ 345.758560] kvm [1491]: vcpu0 unhandled rdmsr: 0x1c9 data 0x0 [ 345.758594] kvm [1491]: vcpu0 unhandled rdmsr: 0x1a6 data 0x0 [ 345.758619] kvm [1491]: vcpu0 unhandled rdmsr: 0x1a7 data 0x0 [ 345.758644] kvm [1491]: vcpu0 unhandled rdmsr: 0x3f6 data 0x0 [ 345.951601] kvm [1493]: vcpu1 unhandled rdmsr: 0x4e data 0x0 [ 351.857036] kvm [1493]: vcpu1 unhandled wrmsr: 0xc90 data 0xfffff
After this commit, -ENOENT is returned to vcpu_enter_guest() causes the userspace to abort.
kvm_msr_ignored_check() kvm_set_msr() kvm_emulate_wrmsr() vmx_handle_exit() vcpu_enter_guest()
Something like below will unbreak the userspace, but does anyone has a better idea?
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1748,7 +1748,7 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu) return 0; /* Signal all other negative errors to userspace */ - if (r < 0) + if (r < 0 && r != -ENOENT) return r; /* MSR write failed? Inject a #GP */
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