linux-kernel - Re: [PATCH v3 1/2] KVM: x86: Check hypercall's exit to userspace generically

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Message-ID: <d7bf51a9-fcbc-4f7a-af5c-459f5c576e3f@intel.com>
Date: Wed, 9 Oct 2024 14:48:49 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: pbonzini@...hat.com, seanjc@...gle.com, isaku.yamahata@...el.com,
 rick.p.edgecombe@...el.com, kai.huang@...el.com, yuan.yao@...ux.intel.com
Subject: Re: [PATCH v3 1/2] KVM: x86: Check hypercall's exit to userspace
 generically

On 8/26/2024 10:22 AM, Binbin Wu wrote:
> Check whether a KVM hypercall needs to exit to userspace or not based on
> hypercall_exit_enabled field of struct kvm_arch.
> 
> Userspace can request a hypercall to exit to userspace for handling by
> enable KVM_CAP_EXIT_HYPERCALL and the enabled hypercall will be set in
> hypercall_exit_enabled.  Make the check code generic based on it.
> 
> Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> ---
>   arch/x86/kvm/x86.c | 5 +++--
>   arch/x86/kvm/x86.h | 4 ++++
>   2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 966fb301d44b..e521f14ad2b2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10220,8 +10220,9 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>   	cpl = kvm_x86_call(get_cpl)(vcpu);
>   
>   	ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
> -	if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
> -		/* MAP_GPA tosses the request to the user space. */
> +	/* Check !ret first to make sure nr is a valid KVM hypercall. */
> +	if (!ret && user_exit_on_hypercall(vcpu->kvm, nr))
> +		/* The hypercall is requested to exit to userspace. */

Nit: Above comment is unnecessary since the name of 
user_exit_on_hypercall() is self documenting.

Otherwise,

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

>   		return 0;
>   
>   	if (!op_64_bit)
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 6556a43f1915..bc1a9e080acb 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -561,4 +561,8 @@ 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