Re: [PATCH 2/3] x86/split_lock: Refactor and export handle_user_split_lock() for KVM

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org, "Kenneth R . Crudup" <kenny@panix.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Xiaoyao Li <xiaoyao.li@intel.com>, Nadav Amit <namit@vmware.com>,
	Thomas Hellstrom <thellstrom@vmware.com>,
	Tony Luck <tony.luck@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jessica Yu <jeyu@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] x86/split_lock: Refactor and export handle_user_split_lock() for KVM
Date: Thu, 2 Apr 2020 10:19:46 -0700	[thread overview]
Message-ID: <20200402171946.GH13879@linux.intel.com> (raw)
In-Reply-To: <87v9mhn7nf.fsf@nanos.tec.linutronix.de>

On Thu, Apr 02, 2020 at 07:01:56PM +0200, Thomas Gleixner wrote:
> Sean Christopherson <sean.j.christopherson@intel.com> writes:
> > From: Xiaoyao Li <xiaoyao.li@intel.com>
> >
> > In the future, KVM will use handle_user_split_lock() to handle #AC
> > caused by split lock in guest. Due to the fact that KVM doesn't have
> > a @regs context and will pre-check EFLAGS.AC, move the EFLAGS.AC check
> > to do_alignment_check().
> >
> > Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > Reviewed-by: Tony Luck <tony.luck@intel.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/include/asm/cpu.h  | 4 ++--
> >  arch/x86/kernel/cpu/intel.c | 7 ++++---
> >  arch/x86/kernel/traps.c     | 2 +-
> >  3 files changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> > index ff6f3ca649b3..ff567afa6ee1 100644
> > --- a/arch/x86/include/asm/cpu.h
> > +++ b/arch/x86/include/asm/cpu.h
> > @@ -43,11 +43,11 @@ unsigned int x86_stepping(unsigned int sig);
> >  #ifdef CONFIG_CPU_SUP_INTEL
> >  extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
> >  extern void switch_to_sld(unsigned long tifn);
> > -extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
> > +extern bool handle_user_split_lock(unsigned long ip);
> >  #else
> >  static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
> >  static inline void switch_to_sld(unsigned long tifn) {}
> > -static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
> > +static inline bool handle_user_split_lock(unsigned long ip)
> 
> This is necessary because VMX can be compiled without CPU_SUP_INTEL?

Ya, it came about when cleaning up the IA32_FEATURE_CONTROL MSR handling
to consolidate duplicate code.

config KVM_INTEL
        tristate "KVM for Intel (and compatible) processors support"
        depends on KVM && IA32_FEAT_CTL

config IA32_FEAT_CTL
        def_bool y
        depends on CPU_SUP_INTEL || CPU_SUP_CENTAUR || CPU_SUP_ZHAOXIN