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

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Date:	Wed, 28 Jan 2015 21:57:17 +0800
From:	Wincy Van <fanwenyi0529@...il.com>
To:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"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

On Wed, Jan 28, 2015 at 9:06 PM, Zhang, Yang Z <yang.z.zhang@...el.com> wrote:
>>>>         __clear_bit(msr, msr_bitmap_nested + 0x000 / f);
>>>
>>>
>>> Anyway, this is not necessary for your current patch. We can consider
>>> it later if there really have other features will use it.
>>>
>>
>> Yep, I know what you mean now, for other msrs which are not forwarded
>> access by a mechanism like virtual-apic page, we should intercept it
>> unconditionally. I think we should ensure the msr can be allowed
>> before call nested_vmx_disable_intercept_for_msr, if L0 want to
>> intercept it, just do not call nested_vmx_disable_intercept_for_msr.
>
> Yes, this is a solution. But I prefer to handle it in nested code path since others may not familiar with nested and may block it by mistake.
>
>>
>>  !test_bit(msr, vmcs01_msr_bitmap) will introduce a problem that some
>> of the msrs will be affcted by vmcs01_msr_bitmap, TMCCT and TPR, for example.
>> Intercept reading for these msrs is okay, but it is not efficient.
>
> TMCCT is always trapped by most VMM. I don't think TPR is trapped in KVM.
>

Oooops. This piece of code made me confused and I was not think about
that words, just forget it.
( * ^ _ ^ * )


                vmx_enable_intercept_msr_read_x2apic(0x802);
                /* TMCCT */
                vmx_enable_intercept_msr_read_x2apic(0x839);
                /* TPR */


If there are any features use it in the future, let's consider about
this, thank you for your patience.


Thanks,
Wincy
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