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

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

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@xxxxxxxxxx>
> > > ---
> > >    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.