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

Xiaoyao Li
2023-03-27T13:49:56Z

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@d8708b 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