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

From: Paolo Bonzini <pbonzini@redhat.com>
To: David Edmondson <david.edmondson@oracle.com>,
	linux-kernel@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>,
	Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Sean Christopherson <seanjc@google.com>,
	kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
	Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH] KVM: x86: dump_vmcs should not assume GUEST_IA32_EFER is valid
Date: Thu, 18 Feb 2021 12:54:52 +0100	[thread overview]
Message-ID: <708f2956-fa0f-b008-d3d2-93067f95783c@redhat.com> (raw)
In-Reply-To: <20210218100450.2157308-1-david.edmondson@oracle.com>

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?

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 */
> 