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(-)