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 10:37:50 +0200
From:   Mathias Krause <minipli@...ecurity.net>
To:     Xiaoyao Li <xiaoyao.li@...el.com>, 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 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:

[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