Re: [PATCH] KVM: x86: dump_vmcs should not assume GUEST_IA32_EFER is valid

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/02/21 13:56, David Edmondson wrote:
> On Thursday, 2021-02-18 at 12:54:52 +01, Paolo Bonzini wrote:
> 
>> On 18/02/21 11:04, David Edmondson wrote:
>>> When dumping the VMCS, retrieve the current guest value of EFER from
>>> the kvm_vcpu structure if neither VM_EXIT_SAVE_IA32_EFER or
>>> VM_ENTRY_LOAD_IA32_EFER is set, which can occur if the processor does
>>> not support the relevant VM-exit/entry controls.
>>
>> Printing vcpu->arch.efer is not the best choice however.  Could we dump
>> the whole MSR load/store area instead?
> 
> I'm happy to do that, and think that it would be useful, but it won't
> help with the original problem (which I should have explained more).
> 
> If the guest has EFER_LMA set but we aren't using the entry/exit
> controls, vm_read64(GUEST_IA32_EFER) returns 0, causing dump_vmcs() to
> erroneously dump the PDPTRs.

Got it now.  It would sort of help, because while dumping the MSR 
load/store area you could get hold of the real EFER, and use it to 
decide whether to dump the PDPTRs.

Thanks,

Paolo


>> Paolo
>>
>>> Fixes: 4eb64dce8d0a ("KVM: x86: dump VMCS on invalid entry")
>>> Signed-off-by: David Edmondson <david.edmondson@oracle.com>
>>> ---
>>>    arch/x86/kvm/vmx/vmx.c | 14 +++++++++-----
>>>    arch/x86/kvm/vmx/vmx.h |  2 +-
>>>    2 files changed, 10 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>>> index eb69fef57485..74ea4fe6f35e 100644
>>> --- a/arch/x86/kvm/vmx/vmx.c
>>> +++ b/arch/x86/kvm/vmx/vmx.c
>>> @@ -5754,7 +5754,7 @@ static void vmx_dump_dtsel(char *name, uint32_t limit)
>>>    	       vmcs_readl(limit + GUEST_GDTR_BASE - GUEST_GDTR_LIMIT));
>>>    }
>>>    
>>> -void dump_vmcs(void)
>>> +void dump_vmcs(struct kvm_vcpu *vcpu)
>>>    {
>>>    	u32 vmentry_ctl, vmexit_ctl;
>>>    	u32 cpu_based_exec_ctrl, pin_based_exec_ctrl, secondary_exec_control;
>>> @@ -5771,7 +5771,11 @@ void dump_vmcs(void)
>>>    	cpu_based_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
>>>    	pin_based_exec_ctrl = vmcs_read32(PIN_BASED_VM_EXEC_CONTROL);
>>>    	cr4 = vmcs_readl(GUEST_CR4);
>>> -	efer = vmcs_read64(GUEST_IA32_EFER);
>>> +	if ((vmexit_ctl & VM_EXIT_SAVE_IA32_EFER) ||
>>> +	    (vmentry_ctl & VM_ENTRY_LOAD_IA32_EFER))
>>> +		efer = vmcs_read64(GUEST_IA32_EFER);
>>> +	else
>>> +		efer = vcpu->arch.efer;
>>>    	secondary_exec_control = 0;
>>>    	if (cpu_has_secondary_exec_ctrls())
>>>    		secondary_exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
>>> @@ -5955,7 +5959,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>>>    	}
>>>    
>>>    	if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
>>> -		dump_vmcs();
>>> +		dump_vmcs(vcpu);
>>>    		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
>>>    		vcpu->run->fail_entry.hardware_entry_failure_reason
>>>    			= exit_reason;
>>> @@ -5964,7 +5968,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>>>    	}
>>>    
>>>    	if (unlikely(vmx->fail)) {
>>> -		dump_vmcs();
>>> +		dump_vmcs(vcpu);
>>>    		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
>>>    		vcpu->run->fail_entry.hardware_entry_failure_reason
>>>    			= vmcs_read32(VM_INSTRUCTION_ERROR);
>>> @@ -6049,7 +6053,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>>>    
>>>    unexpected_vmexit:
>>>    	vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n", exit_reason);
>>> -	dump_vmcs();
>>> +	dump_vmcs(vcpu);
>>>    	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>>>    	vcpu->run->internal.suberror =
>>>    			KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
>>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
>>> index 9d3a557949ac..f8a0ce74798e 100644
>>> --- a/arch/x86/kvm/vmx/vmx.h
>>> +++ b/arch/x86/kvm/vmx/vmx.h
>>> @@ -489,6 +489,6 @@ static inline bool vmx_guest_state_valid(struct kvm_vcpu *vcpu)
>>>    	return is_unrestricted_guest(vcpu) || __vmx_guest_state_valid(vcpu);
>>>    }
>>>    
>>> -void dump_vmcs(void);
>>> +void dump_vmcs(struct kvm_vcpu *vcpu);
>>>    
>>>    #endif /* __KVM_X86_VMX_H */
>>>
> 
> dme.
>