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

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Message-ID: <4a5fd5b4-64b7-726a-57a5-a5c669ce84f6@redhat.com>
Date:   Tue, 5 Nov 2019 12:30:14 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     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:     Xiaoyao Li <xiaoyao.li@...el.com>, 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 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.

>  	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.

Paolo