Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 31 May 2023 17:56:24 -0700
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Andrew Cooper <andrew.cooper3@citrix.com>
Cc:     Jon Kohler <jon@nutanix.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        "kvm @ vger . kernel . org" <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: VMX: remove LFENCE in vmx_spec_ctrl_restore_host()
Message-ID: <20230601005624.ou3iqfbpbsfy3j4e@treble>
References: <20230531150112.76156-1-jon@nutanix.com>
 <20230531231820.trrs2uugc24gegj4@treble>
 <F4BEBCAF-CBFC-4C3E-8B01-2ED84CF2E13A@nutanix.com>
 <20230601004202.63yulqs73kuh3ep6@treble>
 <846dd0c5-d431-e20e-fdb3-a4a26b6a22ca@citrix.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <846dd0c5-d431-e20e-fdb3-a4a26b6a22ca@citrix.com>
Precedence: bulk

On Thu, Jun 01, 2023 at 01:50:48AM +0100, Andrew Cooper wrote:
> On 01/06/2023 1:42 am, Josh Poimboeuf wrote:
> > So each LFENCE has a distinct purpose.  That said, there are no indirect
> > branches or unbalanced RETs between them.
> 
> How lucky are you feeling?
> 
> You're in C at this point, which means the compiler could have emitted a
> call to mem{cpy,cmp}() in place of a simple assignment/comparison.

But it's only unbalanced RETs we're concerned about, per Intel.

-- 
Josh