linux-kernel - RE: [PATCH v3 1/6] KVM: nVMX: Use hardware MSR bitmap

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Date:	Wed, 28 Jan 2015 08:00:25 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	Wincy Van <fanwenyi0529@...il.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"gleb@...nel.org" <gleb@...nel.org>
CC:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Jan Kiszka <jan.kiszka@....de>
Subject: RE: [PATCH v3 1/6] KVM: nVMX: Use hardware MSR bitmap

Wincy Van wrote on 2015-01-24:
> Currently, if L1 enables MSR_BITMAP, we will emulate this feature, all of L2's
> msr access is intercepted by L0. Since many features like virtualize x2apic mode
> has a complicated logic and it is difficult for us to emulate, we should use
> hardware and merge the bitmap.
> 
> This patch introduces nested_vmx_merge_msr_bitmap for future use.
> 
> Signed-off-by: Wincy Van <fanwenyi0529@...il.com>
> ---
>  arch/x86/kvm/vmx.c |   71
> +++++++++++++++++++++++++++++++++++++++++++--------
>  1 files changed, 60 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index c987374..36d0724
> 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -798,6 +798,7 @@ static unsigned long *vmx_msr_bitmap_legacy;
> static unsigned long *vmx_msr_bitmap_longmode;  static unsigned long
> *vmx_msr_bitmap_legacy_x2apic;  static unsigned long
> *vmx_msr_bitmap_longmode_x2apic;
> +static unsigned long *vmx_msr_bitmap_nested;
>  static unsigned long *vmx_vmread_bitmap;  static unsigned long
> *vmx_vmwrite_bitmap;
> 
> @@ -5812,13 +5813,18 @@ static __init int hardware_setup(void)
>                                 (unsigned long
> *)__get_free_page(GFP_KERNEL);
>         if (!vmx_msr_bitmap_longmode_x2apic)
>                 goto out4;
> +
> +       vmx_msr_bitmap_nested = (unsigned long
> *)__get_free_page(GFP_KERNEL);
> +       if (!vmx_msr_bitmap_nested)
> +               goto out5;
> +

Since the nested virtualization is off by default. It's better to allocate the page
only when nested is true. Maybe adding the following check is better:

if (nested) {
        vmx_msr_bitmap_nested = (unsigned long *)__get_free_page(GFP_KERNEL);
        if (!vmx_msr_bitmap_nested)
                goto out5;
}

...snip...

> +
> +/*
> + * Merge L0's and L1's MSR bitmap, return false to indicate that
> + * we do not use the hardware.
> + */
> +static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
> +                                              struct vmcs12
> *vmcs12) {
> +       return false;
> +}
> +

The following patches have nothing to do with the MSR control. Why leave the function empty here?

Best regards,
Yang