| Message ID | 20200502043234.12481-1-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: x86: Misc anti-retpoline optimizations | expand |
On 02/05/20 06:32, Sean Christopherson wrote: > A smattering of optimizations geared toward avoiding retpolines, though > IMO most of the patches are worthwhile changes irrespective of retpolines. > I can split this up into separate patches if desired, outside of the > obvious combos there are no dependencies. Most of them are good stuff anyway, I agree. Since I like to believe that static calls _are_ close, I queued these: KVM: x86: Save L1 TSC offset in 'struct kvm_vcpu_arch' KVM: nVMX: Unconditionally validate CR3 during nested transitions KVM: VMX: Add proper cache tracking for CR4 KVM: VMX: Add proper cache tracking for CR0 KVM: VMX: Move nested EPT out of kvm_x86_ops.get_tdp_level() hook KVM: x86/mmu: Capture TDP level when updating CPUID and I don't disagree with the DR6 one though it can be even improved a bit so I'll send a patch myself. Paolo
On Mon, May 04, 2020 at 03:25:58PM +0200, Paolo Bonzini wrote: > On 02/05/20 06:32, Sean Christopherson wrote: > > A smattering of optimizations geared toward avoiding retpolines, though > > IMO most of the patches are worthwhile changes irrespective of retpolines. > > I can split this up into separate patches if desired, outside of the > > obvious combos there are no dependencies. > > Most of them are good stuff anyway, I agree. > > Since I like to believe that static calls _are_ close, I queued these: > > KVM: x86: Save L1 TSC offset in 'struct kvm_vcpu_arch' > KVM: nVMX: Unconditionally validate CR3 during nested transitions > KVM: VMX: Add proper cache tracking for CR4 > KVM: VMX: Add proper cache tracking for CR0 > KVM: VMX: Move nested EPT out of kvm_x86_ops.get_tdp_level() hook > KVM: x86/mmu: Capture TDP level when updating CPUID > > and I don't disagree with the DR6 one though it can be even improved a > bit so I'll send a patch myself. Sounds good, thanks!
A smattering of optimizations geared toward avoiding retpolines, though IMO most of the patches are worthwhile changes irrespective of retpolines. I can split this up into separate patches if desired, outside of the obvious combos there are no dependencies. I was mainly coming at this from a nVMX angle. On a Haswell, this reduces the best case latency for a nested VMX roundtrip by ~750 cycles, though I doubt that much benefit will be realized in practice. The CR0 and CR4 caching changes in particular are keepers, if only because they get rid of the awful cache vs. decache naming. And the CR4 change can eliminate multiple of VMREADs in the nested VMX paths. Ditto for the CR3 validation patch; it's arguably more readable and can avoid a VMREAD. I like the L1 TSC offset patch because VMX and SVM have inverted logic for how they track the L1 offset, and because math is hard. I think I like the TDP level change even if retpolines didn't exist? The nested EPT behavior is a bit scary, but it was already scary, this just makes it more obvious. The RIP/RSP accessors are definitely obsoleted by static calls, but IMO the noise is worth the benefit unless static calls are imminent. The DR6 change is gratuitous, though I do like not having to dive into the VMX code when I inevitably forget the VMX implementations are nops. Sean Christopherson (10): KVM: x86: Save L1 TSC offset in 'struct kvm_vcpu_arch' KVM: nVMX: Unconditionally validate CR3 during nested transitions KVM: x86: Make kvm_x86_ops' {g,s}et_dr6() hooks optional KVM: x86: Split guts of kvm_update_dr7() to separate helper KVM: nVMX: Avoid retpoline when writing DR7 during nested transitions KVM: VMX: Add proper cache tracking for CR4 KVM: VMX: Add proper cache tracking for CR0 KVM: VMX: Add anti-retpoline accessors for RIP and RSP KVM: VMX: Move nested EPT out of kvm_x86_ops.get_tdp_level() hook KVM: x86/mmu: Capture TDP level when updating CPUID arch/x86/include/asm/kvm_host.h | 7 +-- arch/x86/kvm/cpuid.c | 3 +- arch/x86/kvm/kvm_cache_regs.h | 10 +++-- arch/x86/kvm/mmu/mmu.c | 6 +-- arch/x86/kvm/svm/nested.c | 2 +- arch/x86/kvm/svm/svm.c | 21 --------- arch/x86/kvm/vmx/nested.c | 49 +++++++++++---------- arch/x86/kvm/vmx/vmx.c | 77 +++++++++++++-------------------- arch/x86/kvm/vmx/vmx.h | 30 +++++++++++++ arch/x86/kvm/x86.c | 26 ++++------- arch/x86/kvm/x86.h | 14 ++++++ 11 files changed, 125 insertions(+), 120 deletions(-)