Re: [PATCH 4/6] x86/entry: Optimize local_db_save() for virt

On Thu, May 28, 2020 at 10:19:41PM +0200, Peter Zijlstra wrote: > static int arch_bp_generic_len(int x86_len) > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -3027,6 +3027,8 @@ static int nested_vmx_check_vmentry_hw(s > > /* >* VMExit clears RFLAGS.IF and D

[PATCH 4/6] x86/entry: Optimize local_db_save() for virt

Because DRn access is 'difficult' with virt; but the DR7 read is cheaper than a cacheline miss on native, add a virt specific fast path to local_db_save(), such that when breakpoints are not in use we avoid touching DRn entirely. Suggested-by: Andy Lutomirski Signed-off-by: Peter Zijlstra (Intel)