linux-kernel - Re: [PATCH v4 2/6] KVM: x86: Add a helper to check for user interception of KVM hypercalls

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Message-ID: <83c7a5e4-398c-4610-1412-74e4309aea27@amd.com>
Date: Mon, 2 Dec 2024 12:57:58 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Binbin Wu <binbin.wu@...ux.intel.com>,
 Isaku Yamahata <isaku.yamahata@...el.com>, Kai Huang <kai.huang@...el.com>,
 Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH v4 2/6] KVM: x86: Add a helper to check for user
 interception of KVM hypercalls

On 11/27/24 18:43, Sean Christopherson wrote:
> From: Binbin Wu <binbin.wu@...ux.intel.com>
> 
> Add and use user_exit_on_hypercall() to check if userspace wants to handle
> a KVM hypercall instead of open-coding the logic everywhere.
> 
> No functional change intended.
> 
> Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> Reviewed-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> [sean: squash into one patch, keep explicit KVM_HC_MAP_GPA_RANGE check]
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/kvm/svm/sev.c | 4 ++--
>  arch/x86/kvm/x86.c     | 2 +-
>  arch/x86/kvm/x86.h     | 5 +++++
>  3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 72674b8825c4..6ac6312c4d57 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3640,7 +3640,7 @@ static int snp_begin_psc_msr(struct vcpu_svm *svm, u64 ghcb_msr)
>  		return 1; /* resume guest */
>  	}
>  
> -	if (!(vcpu->kvm->arch.hypercall_exit_enabled & (1 << KVM_HC_MAP_GPA_RANGE))) {
> +	if (!user_exit_on_hypercall(vcpu->kvm, KVM_HC_MAP_GPA_RANGE)) {
>  		set_ghcb_msr(svm, GHCB_MSR_PSC_RESP_ERROR);
>  		return 1; /* resume guest */
>  	}
> @@ -3723,7 +3723,7 @@ static int snp_begin_psc(struct vcpu_svm *svm, struct psc_buffer *psc)
>  	bool huge;
>  	u64 gfn;
>  
> -	if (!(vcpu->kvm->arch.hypercall_exit_enabled & (1 << KVM_HC_MAP_GPA_RANGE))) {
> +	if (!user_exit_on_hypercall(vcpu->kvm, KVM_HC_MAP_GPA_RANGE)) {
>  		snp_complete_psc(svm, VMGEXIT_PSC_ERROR_GENERIC);
>  		return 1;
>  	}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0b2fe4aa04a2..13fe5d6eb8f3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10041,7 +10041,7 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>  		u64 gpa = a0, npages = a1, attrs = a2;
>  
>  		ret = -KVM_ENOSYS;
> -		if (!(vcpu->kvm->arch.hypercall_exit_enabled & (1 << KVM_HC_MAP_GPA_RANGE)))
> +		if (!user_exit_on_hypercall(vcpu->kvm, KVM_HC_MAP_GPA_RANGE))
>  			break;
>  
>  		if (!PAGE_ALIGNED(gpa) || !npages ||
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index ec623d23d13d..45dd53284dbd 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -612,4 +612,9 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
>  			 unsigned int port, void *data,  unsigned int count,
>  			 int in);
>  
> +static inline bool user_exit_on_hypercall(struct kvm *kvm, unsigned long hc_nr)
> +{
> +	return kvm->arch.hypercall_exit_enabled & BIT(hc_nr);
> +}
> +
>  #endif