Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: 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>,
	Peter Zijlstra <peterz@infradead.org>,
	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: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW
Date: Wed, 25 Oct 2023 23:13:46 +0100	[thread overview]
Message-ID: <0ee3e3cd-01b2-4662-ba08-d137663f1699@citrix.com> (raw)
In-Reply-To: <20231025220735.gpopnng76klkbuu3@desk>

On 25/10/2023 11:07 pm, Pawan Gupta wrote:
> On Wed, Oct 25, 2023 at 10:10:41PM +0100, Andrew Cooper wrote:
>>> +.align L1_CACHE_BYTES, 0xcc
>>> +SYM_CODE_START_NOALIGN(mds_verw_sel)
>>> +	UNWIND_HINT_UNDEFINED
>>> +	ANNOTATE_NOENDBR
>>> +	.word __KERNEL_DS
>> You need another .align here.  Otherwise subsequent code will still
>> start in this cacheline and defeat the purpose of trying to keep it
>> separate.
> Right.
>
>>> +SYM_CODE_END(mds_verw_sel);
>> Thinking about it, should this really be CODE and not a data entry?
> Would that require adding a data equivalent of .entry.text and update
> KPTI to keep it mapped? Or is there an easier option?

Leave it right here in .entry.text , but try using SYM_DATA() and
friends.  See whether objtool vomits over the result or not.

And if objtool does vomit over the result, then leaving it as it is in
this patch with SYM_CODE() is good enough.

>
>> P.S. Please CC on the full series.  Far less effort than fishing the
>> rest off lore.
> I didn't realize get_maintainer.pl isn't doing that already. Proposing
> below update to MAINTAINERS:
>
> ---
> From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Date: Wed, 25 Oct 2023 14:50:41 -0700
> Subject: [PATCH] MAINTAINERS: Update entry for X86 HARDWARE VULNERABILITIES
>
> Add Andrew Cooper to maintainers of hardware vulnerabilities
> mitigations.
>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> ---
>  MAINTAINERS | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2894f0777537..bf8c8707b8f8 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -23382,6 +23382,7 @@ M:	Thomas Gleixner <tglx@linutronix.de>
>  M:	Borislav Petkov <bp@alien8.de>
>  M:	Peter Zijlstra <peterz@infradead.org>
>  M:	Josh Poimboeuf <jpoimboe@kernel.org>
> +M:	Andrew Cooper <andrew.cooper3@citrix.com>

Oh, right.  Perhaps R rather than M seeing as I can't make any time
commitments, but sure.

~Andrew