Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.31 as permitted sender) client-ip=23.128.96.31;
Date:   Wed, 25 Oct 2023 10:02:13 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrew Cooper <andrew.cooper3@citrix.com>
Cc:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>, tony.luck@intel.com,
        ak@linux.intel.com, tim.c.chen@linux.intel.com,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        kvm@vger.kernel.org,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        antonio.gomez.iglesias@linux.intel.com,
        Alyssa Milburn <alyssa.milburn@intel.com>
Subject: Re: [RESEND][PATCH 1/6] x86/bugs: Add asm helpers for executing VERW
Message-ID: <20231025080213.GC37471@noisy.programming.kicks-ass.net>
References: <20231020-delay-verw-v1-0-cff54096326d@linux.intel.com>
 <20231020-delay-verw-v1-1-cff54096326d@linux.intel.com>
 <f620c7d4-6345-4ad0-8a45-c8089e3c34df@citrix.com>
 <20231025062818.7kaerqklaut7dg5r@desk>
 <20231025072255.GA37471@noisy.programming.kicks-ass.net>
 <654468cf-1563-4c1c-8c7c-076bc6dfbabf@citrix.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <654468cf-1563-4c1c-8c7c-076bc6dfbabf@citrix.com>
Precedence: bulk

On Wed, Oct 25, 2023 at 08:52:50AM +0100, Andrew Cooper wrote:

> > +.pushsection .entry.text, "ax"
> > +
> > +.align 64
> > +SYM_CODE_START_NOALIGN(mds_verw_sel)
> > +	UNWIND_HINT_UNDEFINED
> > +	ANNOTATE_NOENDBR
> > +1:
> > +	.word __KERNEL_DS
> > +	.skip 64 - (. - 1b), 0xcc
> 
> The 1 label aliases mds_verw_sel and this must remain like this for the
> construct to work.
> 
> So instead of .skip, why not simply .align 64, 0xcc and get rid of the
> 1: label?

Because I forgot you can add a filler byte to .align :/ Yes, that's much
saner.

> Do we have a suitably named constant cacheline size, rather than
> opencoding 64?

L1_CACHE_BYTES probably.

> 
> > +SYM_CODE_END(mds_verw_sel);
> 
> Given that KVM needs it, this probably needs an EXPORT_SYMBOL_GPL() on it.

localyesconfig ftw ;-)

/me runs