linux-kernel - Re: [PATCH] KVM: x86: Add host physical address width capability

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Date:	Thu, 9 Jul 2015 08:09:30 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org
Cc:	Laszlo Ersek <lersek@...hat.com>, linux-kernel@...r.kernel.org,
	qemu-devel@...gnu.org
Subject: Re: [PATCH] KVM: x86: Add host physical address width capability



On 09/07/2015 00:36, Bandan Das wrote:
> Let userspace inquire the maximum physical address width
> of the host processors; this can be used to identify maximum
> memory that can be assigned to the guest.
> 
> Reported-by: Laszlo Ersek <lersek@...hat.com>
> Signed-off-by: Bandan Das <bsd@...hat.com>
> ---
>  arch/x86/kvm/x86.c       | 3 +++
>  include/uapi/linux/kvm.h | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbaf44e..97d6746 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2683,6 +2683,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_NR_MEMSLOTS:
>  		r = KVM_USER_MEM_SLOTS;
>  		break;
> +	case KVM_CAP_PHY_ADDR_WIDTH:
> +		r = boot_cpu_data.x86_phys_bits;
> +		break;

Userspace can just use CPUID, can't it?

Paolo

>  	case KVM_CAP_PV_MMU:	/* obsolete */
>  		r = 0;
>  		break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 716ad4a..e7949a1 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_DISABLE_QUIRKS 116
>  #define KVM_CAP_X86_SMM 117
>  #define KVM_CAP_MULTI_ADDRESS_SPACE 118
> +#define KVM_CAP_PHY_ADDR_WIDTH 119
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> 
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