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

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Message-ID: <cuntuq9ilg4.fsf@dme.org>
Date:   Thu, 18 Feb 2021 12:56:11 +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 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.

> 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.
-- 
Why stay in college? Why go to night school?