Messages in this thread | | | From | Vitaly Kuznetsov <> | Subject | [PATCH RFC 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs | Date | Fri, 2 Mar 2018 11:55:00 +0100 |
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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
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