RFC x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs
Get series with b4
b4 am [email protected]Versions newest first
- v1 RFC Latest3 patches 6 repliesIn review
Patches in v1 No applies recorded yet
| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/3 | x86/kvm/vmx: read MSR_FS_BASE from current->threadarch/ | +1 | 3 replies | |
| 2/3 | x86/kvm/vmx: read MSR_KERNEL_GS_BASE from current->threadarch/ | +1 | 0 replies | |
| 3/3 | x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASEarch/ arch/ | +3 | 2 replies |
Reviews trailers per patch
No Reviewed-by, Acked-by or Tested-by trailers for v1 yet.
Cover letter [PATCH RFC 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs
Some time ago Paolo suggested to take a look at probably unneeded expensive rdmsrs for FS/GS base MSR in vmx_save_host_state(). This is called on every vcpu run when we need to handle vmexit in userspace.
I have to admit I got a bit lost in our kernel FS/GS magic. I managed to convince myself that in the well defined context (ioctl from userspace) we can always get the required values from in-kernel variables and avoid rdmsrs. But I may have missed something really important, thus RFC.
My debug shows we're shaving off 240 cpu cycles (E5-2603 v3).
In case these patches turn out to be worthwile AMD SVM can probably be optimized the ame way.
Vitaly Kuznetsov (3):
x86/kvm/vmx: read MSR_FS_BASE from current->thread x86/kvm/vmx: read MSR_KERNEL_GS_BASE from current->thread x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE
arch/x86/kernel/cpu/common.c | 1 + arch/x86/kvm/vmx.c | 7 ++++--- 2 files changed, 5 insertions(+), 3 deletions(-)
Signature · 1 line
2.14.3