[v2,0/3] VMX: more nested fixes

Message

Maxim Levitsky Jan. 14, 2021, 8:54 p.m. UTC

This is hopefully the last fix for VMX nested migration
that finally allows my stress test of migration with a nested guest to pass.

In a nutshell after an optimization that was done in commit 7952d769c29ca,
some of vmcs02 fields which can be modified by the L2 freely while it runs
(like GSBASE and such) were not copied back to vmcs12 unless:

1. L1 tries to vmread them (update done on intercept)
2. vmclear or vmldptr on other vmcs are done.
3. nested state is read and nested guest is running.

What wasn't done was to sync these 'rare' fields when L1 is running
but still has a loaded vmcs12 which might have some stale fields,
if that vmcs was used to enter a guest already due to that optimization.

Plus I added two minor patches to improve VMX tracepoints
a bit. There is still a large room for improvement.

Best regards,
	Maxim Levitsky

Maxim Levitsky (3):
  KVM: nVMX: Always call sync_vmcs02_to_vmcs12_rare on migration
  KVM: nVMX: add kvm_nested_vmlaunch_resume tracepoint
  KVM: VMX: read idt_vectoring_info a bit earlier

 arch/x86/kvm/trace.h      | 30 ++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/nested.c | 19 ++++++++++++++-----
 arch/x86/kvm/vmx/vmx.c    |  3 ++-
 arch/x86/kvm/x86.c        |  1 +
 4 files changed, 47 insertions(+), 6 deletions(-)

Comments

Paolo Bonzini Jan. 21, 2021, 3 p.m. UTC | #1

On 14/01/21 21:54, Maxim Levitsky wrote:
> This is hopefully the last fix for VMX nested migration
> that finally allows my stress test of migration with a nested guest to pass.
> 
> In a nutshell after an optimization that was done in commit 7952d769c29ca,
> some of vmcs02 fields which can be modified by the L2 freely while it runs
> (like GSBASE and such) were not copied back to vmcs12 unless:
> 
> 1. L1 tries to vmread them (update done on intercept)
> 2. vmclear or vmldptr on other vmcs are done.
> 3. nested state is read and nested guest is running.
> 
> What wasn't done was to sync these 'rare' fields when L1 is running
> but still has a loaded vmcs12 which might have some stale fields,
> if that vmcs was used to enter a guest already due to that optimization.
> 
> Plus I added two minor patches to improve VMX tracepoints
> a bit. There is still a large room for improvement.
> 
> Best regards,
> 	Maxim Levitsky
> 
> Maxim Levitsky (3):
>    KVM: nVMX: Always call sync_vmcs02_to_vmcs12_rare on migration
>    KVM: nVMX: add kvm_nested_vmlaunch_resume tracepoint
>    KVM: VMX: read idt_vectoring_info a bit earlier
> 
>   arch/x86/kvm/trace.h      | 30 ++++++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/nested.c | 19 ++++++++++++++-----
>   arch/x86/kvm/vmx/vmx.c    |  3 ++-
>   arch/x86/kvm/x86.c        |  1 +
>   4 files changed, 47 insertions(+), 6 deletions(-)
> 

I committed patch 1 since I need to send it out to Linus quite soonish, 
but please adjust and resend the others based on Sean's review.

Paolo