Messages in this thread Patch in this message | | | Subject | Re: [PATCH] KVM: VMX: Check if bus lock vmexit was preempted | From | Xiaoyao Li <> | Date | Wed, 22 Sep 2021 18:32:22 +0800 |
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On 9/22/2021 6:02 PM, Paolo Bonzini wrote: > On 18/09/21 13:30, Hao Xiang wrote: >> exit_reason.bus_lock_detected is not only set when bus lock VM exit >> was preempted, in fact, this bit is always set if bus locks are >> detected no matter what the exit_reason.basic is. >> >> So the bus_lock_vmexit handling in vmx_handle_exit should be duplicated >> when exit_reason.basic is EXIT_REASON_BUS_LOCK(74). We can avoid it by >> checking if bus lock vmexit was preempted in vmx_handle_exit. > > I don't understand, does this mean that bus_lock_detected=1 if > basic=EXIT_REASON_BUS_LOCK? If so, can we instead replace the contents > of handle_bus_lock_vmexit with > > /* Do nothing and let vmx_handle_exit exit to userspace. */ > WARN_ON(!to_vmx(vcpu)->exit_reason.bus_lock_detected); > return 0; > > ? > > That would be doable only if this is architectural behavior and not a > processor erratum, of course.
EXIT_REASON.bus_lock_detected may or may not be set when exit reason == EXIT_REASON_BUS_LOCK. Intel will update ISE or SDM to state it.
Maybe we can do below in handle_bus_lock_vmexit handler:
if (!to_vmx(vcpu)->exit_reason.bus_lock_detected) to_vmx(vcpu)->exit_reason.bus_lock_detected = 1;
But is manually changing the hardware reported value for software purpose a good thing?
> Thanks, > > Paolo > >> Signed-off-by: Hao Xiang <hao.xiang@linux.alibaba.com> >> --- >> arch/x86/kvm/vmx/vmx.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >> index 0c2c0d5..5ddf1df 100644 >> --- a/arch/x86/kvm/vmx/vmx.c >> +++ b/arch/x86/kvm/vmx/vmx.c >> @@ -6054,7 +6054,8 @@ static int vmx_handle_exit(struct kvm_vcpu >> *vcpu, fastpath_t exit_fastpath) >> * still need to exit to user space when bus lock detected to >> inform >> * that there is a bus lock in guest. >> */ >> - if (to_vmx(vcpu)->exit_reason.bus_lock_detected) { >> + if (to_vmx(vcpu)->exit_reason.bus_lock_detected && >> + to_vmx(vcpu)->exit_reason.basic != EXIT_REASON_BUS_LOCK) { >> if (ret > 0) >> vcpu->run->exit_reason = KVM_EXIT_X86_BUS_LOCK; >> >
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