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(-) -- 2.14.3
