On Sat, Mar 25, 2023 at 12:39:59PM +0100, Mathias Krause wrote:
On 23.03.23 23:50, Sean Christopherson wrote:
On Wed, 22 Mar 2023 02:37:25 +0100, Mathias Krause wrote:
v3: https://lore.kernel.org/kvm/20230201194604.11135-1-minipli@grsecurity.net/
This series is the fourth iteration of resurrecting the missing pieces of Paolo's previous attempt[1] to avoid needless MMU roots unloading.
It's incorporating Sean's feedback to v3 and rebased on top of kvm-x86/next, namely commit d8708b80fa0e ("KVM: Change return type of kvm_arch_vm_ioctl() to "int"").
[...]
Applied 1 and 5 to kvm-x86 mmu, and the rest to kvm-x86 misc, thanks!
[1/6] KVM: x86/mmu: Avoid indirect call for get_cr3 https://github.com/kvm-x86/linux/commit/2fdcc1b32418 [2/6] KVM: x86: Do not unload MMU roots when only toggling CR0.WP with TDP enabled https://github.com/kvm-x86/linux/commit/01b31714bd90 [3/6] KVM: x86: Ignore CR0.WP toggles in non-paging mode https://github.com/kvm-x86/linux/commit/e40bcf9f3a18 [4/6] KVM: x86: Make use of kvm_read_cr*_bits() when testing bits https://github.com/kvm-x86/linux/commit/74cdc836919b [5/6] KVM: x86/mmu: Fix comment typo https://github.com/kvm-x86/linux/commit/50f13998451e [6/6] KVM: VMX: Make CR0.WP a guest owned bit https://github.com/kvm-x86/linux/commit/fb509f76acc8
Thanks a lot, Sean!
As this is a huge performance fix for us, we'd like to get it integrated into current stable kernels as well -- not without having the changes get some wider testing, of course, i.e. not before they end up in a non-rc version released by Linus. But I already did a backport to 5.4 to get a feeling how hard it would be and for the impact it has on older kernels.
Using the 'ssdd 10 50000' test I used before, I get promising results there as well. Without the patches it takes 9.31s, while with them we're down to 4.64s. Taking into account that this is the runtime of a workload in a VM that gets cut in half, I hope this qualifies as stable material, as it's a huge performance fix.
Greg, what's your opinion on it? Original series here: https://lore.kernel.org/kvm/20230322013731.102955-1-minipli@grsecurity.net/
I'll leave the judgement call up to the KVM maintainers, as they are the ones that need to ack any KVM patch added to stable trees.
thanks,
greg k-h