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

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Message-ID: <a0757b84-1a68-44c9-972a-1d6cc72b6a09@linux.intel.com>
Date: Wed, 14 Aug 2024 09:08:20 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.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 8/14/2024 7:16 AM, Huang, Kai wrote:
>
>
> 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.
>
>
Yes, check "!ret" first to make sure the input of 
is_kvm_hc_exit_enabled() is a valid KVM_HC_*.
Will add a comment.
Thanks.