linux-kernel - Re: [PATCH 02/29] x86/module: Fix the paravirt vs alternative order

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Date:   Fri, 18 Feb 2022 12:28:20 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH 02/29] x86/module: Fix the paravirt vs alternative order

On Fri, Feb 18, 2022 at 05:49:04PM +0100, Peter Zijlstra wrote:
> Ever since commit 4e6292114c741 ("x86/paravirt: Add new features for
> paravirt patching") there is an ordering dependency between patching
> paravirt ops and patching alternatives, the module loader still
> violates this.
> 
> Fixes: 4e6292114c741 ("x86/paravirt: Add new features for paravirt patching")
> Cc: Juergen Gross <jgross@...e.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Probably a good idea to put the 'para' and 'alt' clauses next to each
other and add a comment that the ordering is necessary.

> ---
>  arch/x86/kernel/module.c |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -272,6 +272,10 @@ int module_finalize(const Elf_Ehdr *hdr,
>  			retpolines = s;
>  	}
>  
> +	if (para) {
> +		void *pseg = (void *)para->sh_addr;
> +		apply_paravirt(pseg, pseg + para->sh_size);
> +	}
>  	if (retpolines) {
>  		void *rseg = (void *)retpolines->sh_addr;
>  		apply_retpolines(rseg, rseg + retpolines->sh_size);
> @@ -289,11 +293,6 @@ int module_finalize(const Elf_Ehdr *hdr,
>  					    tseg, tseg + text->sh_size);
>  	}
>  
> -	if (para) {
> -		void *pseg = (void *)para->sh_addr;
> -		apply_paravirt(pseg, pseg + para->sh_size);
> -	}
> -
>  	/* make jump label nops */
>  	jump_label_apply_nops(me);
>  
> 
> 

-- 
Josh