linux-kernel - Re: [PATCH v4 03/16] x86/alternatives: Disable LASS when patching kernel alternatives

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Message-ID: <20240710171836.GGZo7CbFJeZwLCZUAt@fat_crate.local>
Date: Wed, 10 Jul 2024 19:18:36 +0200
From: Borislav Petkov <bp@...en8.de>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ard Biesheuvel <ardb@...nel.org>,
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	Xiongwei Song <xiongwei.song@...driver.com>,
	Xin Li <xin3.li@...el.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>,
	Brijesh Singh <brijesh.singh@....com>,
	Michael Roth <michael.roth@....com>,
	Tony Luck <tony.luck@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Alexey Kardashevskiy <aik@....com>,
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	Sohil Mehta <sohil.mehta@...el.com>, Ingo Molnar <mingo@...nel.org>,
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	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v4 03/16] x86/alternatives: Disable LASS when patching
 kernel alternatives

On Wed, Jul 10, 2024 at 07:06:39PM +0300, Alexander Shishkin wrote:
>  static void text_poke_memcpy(void *dst, const void *src, size_t len)
>  {
> -	memcpy(dst, src, len);
> +	stac();
> +	__inline_memcpy(dst, src, len);
> +	clac();

I think you need LASS-specific stac()/clac() or an alternative_2 or so. You
can't cause that perf penalty on !LASS machines.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette