Re: [PATCH 0/6] KVM TSS cleanups and speedups
From: Paolo Bonzini
Date: Mon Feb 20 2017 - 12:52:48 EST
On 20/02/2017 17:56, Andy Lutomirski wrote:
> The first four patches here are intended to be straightforward
> cleanups and to make a better base for Thomas' GDT series. They may
> be a slight speedup, too, because they remove an STR instruction
> from the VMX entry path.
> The last two patches are a reasonably large speedup but need careful
I spotted (I think) a bug in patch 6, but apart from that it looks nice.
> FWIW, I can see lots of additional easy-ish speedups here. For example:
> - The GDT reload on VM exit isn't really needed at all. Instead let's
> just change the kernel limit to 0xFFFF. Doing that naively would
> waste memory, but doing it carefully on top of Thomas' series would
> be straightforward and almost free.
> - RDMSR from MSR_GS_BASE is totally pointless.
> - Once I or someone finishes the FSGSBASE series, we get a big speedup
> - The LDT reload code should be split up and optimized better, I think.
> Andy Lutomirski (6):
> x86/asm: Define the kernel TSS limit in a macro
> x86/kvm/vmx: Don't fetch the TSS base from the GDT
> x86/kvm/vmx: Get rid of segment_base() on 64-bit kernels
> x86/kvm/vmx: Simplify segment_base()
> x86/asm/64: Drop __cacheline_aligned from struct x86_hw_tss
> x86/kvm/vmx: Defer TR reload after VM exit
> arch/x86/include/asm/desc.h | 58 ++++++++++++++++++++++++++++++------
> arch/x86/include/asm/processor.h | 12 +++++++-
> arch/x86/kernel/ioport.c | 5 ++++
> arch/x86/kernel/process.c | 10 +++++++
> arch/x86/kvm/vmx.c | 63 +++++++++++++++++-----------------------
> 5 files changed, 102 insertions(+), 46 deletions(-)