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

Mathias Krause
2023-03-27T08:42:27Z

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@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