linux-kernel - Re: [PATCH v4 6/6] KVM: VMX: Make CR0.WP a guest owned bit

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Date:   Mon, 27 Mar 2023 21:48:01 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Mathias Krause <minipli@...ecurity.net>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 6/6] KVM: VMX: Make CR0.WP a guest owned bit

On 3/27/2023 4:37 PM, Mathias Krause wrote:
> On 27.03.23 10:33, Xiaoyao Li wrote:
>> On 3/22/2023 9:37 AM, Mathias Krause wrote:
>>> Guests like grsecurity that make heavy use of CR0.WP to implement kernel
>>> level W^X will suffer from the implied VMEXITs.
>>>
>>> With EPT there is no need to intercept a guest change of CR0.WP, so
>>> simply make it a guest owned bit if we can do so.
>>
>> I'm interested in the performance gain. Do you have data like Patch 2?
> 
> It's mentioned in the cover letter[1], quoted below:

Sorry I missed it. The data of not intercepting CR0.WP looks great as well.

> [1]
> https://lore.kernel.org/kvm/20230322013731.102955-1-minipli@grsecurity.net/
> 
> : I used 'ssdd 10 50000' from rt-tests[5] as a micro-benchmark, running on a
> : grsecurity L1 VM. Below table shows the results (runtime in seconds, lower
> : is better):
> :
> :                               legacy     TDP    shadow
> :     kvm-x86/next@...08b        8.43s    9.45s    70.3s
> :     + patches 1-3              5.39s    5.63s    70.2s
> :     + patches 4-6              3.51s    3.47s    67.8s
> 
> 
> Thanks,
> Mathias