linux-kernel - Re: [PATCH] KVM: X86: Dynamically allocating MSR number lists(msrs_to_save[], emulated_msrs[], msr_based

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Date:   Wed, 6 Nov 2019 09:01:18 +0800
From:   cqiang <chenyi.qiang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] KVM: X86: Dynamically allocating MSR number
 lists(msrs_to_save[], emulated_msrs[], msr_based_features[])



On 11/5/2019 9:03 PM, Paolo Bonzini wrote:
> On 05/11/19 13:51, Xiaoyao Li wrote:
>> On 11/5/2019 7:30 PM, Paolo Bonzini wrote:
>>> On 05/11/19 10:20, Chenyi Qiang wrote:
>>>> The three msr number lists(msrs_to_save[], emulated_msrs[] and
>>>> msr_based_features[]) are global arrays of kvm.ko, which are
>>>> initialized/adjusted (copy supported MSRs forward to override the
>>>> unsupported MSRs) when installing kvm-{intel,amd}.ko, but it doesn't
>>>> reset these three arrays to their initial value when uninstalling
>>>> kvm-{intel,amd}.ko. Thus, at the next installation, kvm-{intel,amd}.ko
>>>> will initialize the modified arrays with some MSRs lost and some MSRs
>>>> duplicated.
>>>>
>>>> So allocate and initialize these three MSR number lists dynamically when
>>>> installing kvm-{intel,amd}.ko and free them when uninstalling.
>>>>
>>>> Cc: stable@...r.kernel.org
>>>> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
>>>> Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
>>>> ---
>>>>    arch/x86/kvm/x86.c | 86 ++++++++++++++++++++++++++++++----------------
>>>>    1 file changed, 57 insertions(+), 29 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index ff395f812719..08efcf6351cc 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -1132,13 +1132,15 @@ EXPORT_SYMBOL_GPL(kvm_rdpmc);
>>>>     * List of msr numbers which we expose to userspace through
>>>> KVM_GET_MSRS
>>>>     * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
>>>>     *
>>>> - * This list is modified at module load time to reflect the
>>>> + * The three msr number lists(msrs_to_save, emulated_msrs,
>>>> msr_based_features)
>>>> + * are allocated and initialized at module load time and freed at
>>>> unload time.
>>>> + * msrs_to_save is selected from the msrs_to_save_all to reflect the
>>>>     * capabilities of the host cpu. This capabilities test skips MSRs
>>>> that are
>>>> - * kvm-specific. Those are put in emulated_msrs; filtering of
>>>> emulated_msrs
>>>> + * kvm-specific. Those are put in emulated_msrs_all; filtering of
>>>> emulated_msrs
>>>>     * may depend on host virtualization features rather than host cpu
>>>> features.
>>>>     */
>>>>    -static u32 msrs_to_save[] = {
>>>> +const u32 msrs_to_save_all[] = {
>>>
>>> This can remain static.
>>
>> How about static const u32 msrs_to_save_all[] ?
>>
>> Or you think static is enough?
> 
> "static const" is best indeed (that's what I meant, but I wasn't very
> clear).
> 

Yes, considering the read-only property and scope of these arrays, 
"static const" is more accurate. Thanks.

> Paolo
> 
>>>>        MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP,
>>>> MSR_IA32_SYSENTER_EIP,
>>>>        MSR_STAR,
>>>>    #ifdef CONFIG_X86_64
>>>> @@ -1179,9 +1181,10 @@ static u32 msrs_to_save[] = {
>>>>        MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
>>>>    };
>>>>    +static u32 *msrs_to_save;
>>>
>>> You can use ARRAY_SIZE to allocate the destination arrays statically.
>>
>> It's much better, then we don't need to allocation and free.
>>

Got it. Thanks!

>>> Paolo
>>>
>