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Date: Fri, 9 Feb 2024 13:15:15 -0800
From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
	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,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Nikolay Borisov <nik.borisov@suse.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>, stable@kernel.org
Subject: Re: [PATCH  v7 1/6] x86/bugs: Add asm helpers for executing VERW
Message-ID: <20240209211515.kvpnka7znwkcpokf@desk>
References: <20240204-delay-verw-v7-0-59be2d704cb2@linux.intel.com>
 <20240204-delay-verw-v7-1-59be2d704cb2@linux.intel.com>
 <20240209172843.GUZcZgy7EktXgKZQoc@fat_crate.local>
 <20240209190602.skqahxhgbdc5b2ax@desk>
 <20240209195704.GEZcaDkMUR560qafaI@fat_crate.local>
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On Fri, Feb 09, 2024 at 08:57:04PM +0100, Borislav Petkov wrote:
> On Fri, Feb 09, 2024 at 11:06:02AM -0800, Pawan Gupta wrote:
> > (Though, there was a comment on avoiding the macro alltogether, to which
> > I replied that it complicates 32-bit.)
> 
> Hmm, so this seems to build the respective entry_{32,64}.S TUs fine:
> 
> ---
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index e81cabcb758f..7d1e5fe66495 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -313,12 +313,9 @@
>   *
>   * Note: Only the memory operand variant of VERW clears the CPU buffers.
>   */
> -.macro EXEC_VERW
> -	verw _ASM_RIP(mds_verw_sel)
> -.endm
>  
>  .macro CLEAR_CPU_BUFFERS
> -	ALTERNATIVE "", __stringify(EXEC_VERW), X86_FEATURE_CLEAR_CPU_BUF
> +	ALTERNATIVE "",  __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF
>  .endm

> +.macro CLEAR_CPU_BUFFERS
> +     ALTERNATIVE "", __stringify(EXEC_VERW), X86_FEATURE_CLEAR_CPU_BUF
> +.endm

This works, thanks.

My mistake that I tried your earlier suggestion without playing with it:

  > > +.macro CLEAR_CPU_BUFFERS
  > > +   ALTERNATIVE "", __stringify(EXEC_VERW), X86_FEATURE_CLEAR_CPU_BUF
  > > +.endm
  >
  > Why can't this simply be:
  >
  > .macro CLEAR_CPU_BUFFERS
  >         ALTERNATIVE "", "verw mds_verw_sel(%rip)", X86_FEATURE_CLEAR_CPU_BUF
  > .endm
  >
  > without that silly EXEC_VERW macro?
  >
  > --
  > Regards/Gruss,
  >     Boris.