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

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Date:   Tue, 5 Nov 2019 20:51:51 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Chenyi Qiang <chenyi.qiang@...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 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?

>>   	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.

> Paolo
>