linux-kernel - Re: [PATCH] x86/lam: Disable ADDRESS

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Date: Fri, 19 Jan 2024 09:48:14 -0800
From: Sohil Mehta <sohil.mehta@...el.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>
CC: "H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<kirill.shutemov@...ux.intel.com>, <daniel.sneddon@...ux.intel.com>,
	<antonio.gomez.iglesias@...ux.intel.com>, <rick.p.edgecombe@...el.com>,
	<alexander.shishkin@...el.com>
Subject: Re: [PATCH] x86/lam: Disable ADDRESS_MASKING in most cases

Hi Pawan,

On 1/18/2024 6:35 PM, Pawan Gupta wrote:
>  arch/x86/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 1566748f16c4..794517df8068 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2270,6 +2270,7 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING
>  config ADDRESS_MASKING
>  	bool "Linear Address Masking support"
>  	depends on X86_64
> +	depends on COMPILE_TEST || !SPECULATION_MITIGATIONS # wait for LASS

I was wondering if the COMPILE_TEST dependency here is a bit redundant.

Having ADDRESS_MASKING depend on just !SPECULATION_MITIGATIONS might be
enough to get the LAM code compile tested through various configurations.

I don't have a strong preference here. Mainly looking to understand the
reasoning. Other than that the patch looks fine to me.

Sohil

>  	help
>  	  Linear Address Masking (LAM) modifies the checking that is applied
>  	  to 64-bit linear addresses, allowing software to use of the