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 14:03:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.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 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).

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.
> 
>> Paolo
>>