linux-kernel - Re: [PATCH] KVM: vmx: fix VPID is 0000H in non-root operation

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Date:	Wed, 16 Sep 2015 14:32:33 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Wanpeng Li <wanpeng.li@...mail.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Bandan Das <bsd@...hat.com>, Wincy Van <fanwenyi0529@...il.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: vmx: fix VPID is 0000H in non-root operation

On 2015-09-16 13:31, Wanpeng Li wrote:
> Reference SDM 28.1:
> 
> The current VPID is 0000H in the following situations:
> — Outside VMX operation. (This includes operation in system-management 
>   mode under the default treatment of SMIs and SMM with VMX operation; 
>   see Section 34.14.)
> — In VMX root operation.
> — In VMX non-root operation when the “enable VPID” VM-execution control 
>   is 0.
> 
> The VPID should never be 0000H in non-root operation when "enable VPID" 
> VM-execution control is 1. However, commit (34a1cd60: 'kvm: x86: vmx: 
> move some vmx setting from vmx_init() to hardware_setup()') remove the 
> codes which reserve 0000H for VMX root operation. 
> 
> This patch fix it by reintroducing reserve 0000H for VMX root operation.
> 
> Reported-by: Wincy Van <fanwenyi0529@...il.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/vmx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9ff6a3f..a63b9ca 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6056,6 +6056,8 @@ static __init int hardware_setup(void)
>  	memcpy(vmx_msr_bitmap_longmode_x2apic,
>  			vmx_msr_bitmap_longmode, PAGE_SIZE);
>  
> +	set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */
> +
>  	if (enable_apicv) {
>  		for (msr = 0x800; msr <= 0x8ff; msr++)
>  			vmx_disable_intercept_msr_read_x2apic(msr);
> 

Good point.

BTW, what will happen if allocate_vpid runs out of free slots and
returns 0? Will we always fail then...?

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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