linux-kernel - Re: [PATCH v2 1/2] KVM: x86: Check hypercall's exit to userspace generically

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Message-ID: <d7ae5009-748f-4aa2-937e-d805a3172216@intel.com>
Date: Wed, 14 Aug 2024 11:16:44 +1200
From: "Huang, Kai" <kai.huang@...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>, <michael.roth@....com>
Subject: Re: [PATCH v2 1/2] KVM: x86: Check hypercall's exit to userspace
 generically



On 13/08/2024 5:12 pm, 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>

One nitpicking below:

> ---
>   arch/x86/kvm/x86.c | 4 ++--
>   arch/x86/kvm/x86.h | 7 +++++++
>   2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index af6c8cf6a37a..6e16c9751af7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10226,8 +10226,8 @@ 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. */
> +	if (!ret && is_kvm_hc_exit_enabled(vcpu->kvm, nr))
> +		/* The hypercall is requested to exit to userspace. */
>   		return 0;

I believe you put "!ret" check first for a reason?  Perhaps you can add 
a comment.