linux-kernel - Re: [PATCH] KVM: x86: dump_vmcs should not assume GUEST_IA32

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Message-ID: <cunr1ldikg5.fsf@dme.org>
Date:   Thu, 18 Feb 2021 13:17:46 +0000
From:   David Edmondson <dme@....org>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>, Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: x86: dump_vmcs should not assume GUEST_IA32_EFER
 is valid

On Thursday, 2021-02-18 at 14:01:40 +01, Paolo Bonzini wrote:

> 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.

Okay, I'll do that and come back. Thanks!

> Thanks,
>
> Paolo
>
>
>>> Paolo
>>>
>>>> Fixes: 4eb64dce8d0a ("KVM: x86: dump VMCS on invalid entry")
>>>> Signed-off-by: David Edmondson <david.edmondson@...cle.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.
>> 

dme.
-- 
But he said, leave me alone, I'm a family man.