linux-kernel - Re: [PATCH 02/26] KVM: x86: Take an unsigned 32-bit int for has_emulated

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Date:   Wed, 05 Feb 2020 15:30:59 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 02/26] KVM: x86: Take an unsigned 32-bit int for has_emulated_msr()'s index

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Take a u32 for the index in has_emulated_msr() to match hardware, which
> treats MSR indices as unsigned 32-bit values.  Functionally, taking a
> signed int doesn't cause problems with the current code base, but could
> theoretically cause problems with 32-bit KVM, e.g. if the index were
> checked via a less-than statement, which would evaluate incorrectly for
> MSR indices with bit 31 set.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  arch/x86/kvm/svm.c              | 2 +-
>  arch/x86/kvm/vmx/vmx.c          | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 77d206a93658..5c2ad3fa0980 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1050,7 +1050,7 @@ struct kvm_x86_ops {
>  	int (*hardware_setup)(void);               /* __init */
>  	void (*hardware_unsetup)(void);            /* __exit */
>  	bool (*cpu_has_accelerated_tpr)(void);
> -	bool (*has_emulated_msr)(int index);
> +	bool (*has_emulated_msr)(u32 index);
>  	void (*cpuid_update)(struct kvm_vcpu *vcpu);
>  
>  	struct kvm *(*vm_alloc)(void);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index bf0556588ad0..a7b944a3a0e2 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5985,7 +5985,7 @@ static bool svm_cpu_has_accelerated_tpr(void)
>  	return false;
>  }
>  
> -static bool svm_has_emulated_msr(int index)
> +static bool svm_has_emulated_msr(u32 index)
>  {
>  	switch (index) {
>  	case MSR_IA32_MCG_EXT_CTL:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 1419c53aed16..f5bb1ad2e9fa 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6274,7 +6274,7 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu,
>  		*exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
>  }
>  
> -static bool vmx_has_emulated_msr(int index)
> +static bool vmx_has_emulated_msr(u32 index)
>  {
>  	switch (index) {
>  	case MSR_IA32_SMBASE:

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly