linux-kernel - Re: [PATCHv9 16/16] x86: Re-enable Linear Address Masking

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Message-ID: <b1408df7-abb4-4ac5-aff7-c04fda7dec7c@intel.com>
Date: Tue, 8 Jul 2025 22:31:05 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andy Lutomirski
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Subject: Re: [PATCHv9 16/16] x86: Re-enable Linear Address Masking

On 7/7/2025 1:03 AM, Kirill A. Shutemov wrote:
> This reverts commit 3267cb6d3a174ff83d6287dcd5b0047bbd912452.
> 
> LASS mitigates the Spectre based on LAM (SLAM) [1] and the previous
> commit made LAM depend on LASS, so we no longer need to disable LAM at
> compile time, so revert the commit that disables LAM.
> 

Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>

You may have missed my comments in the previous revision.
https://lore.kernel.org/all/af709ffa-eb11-4de5-9ae8-a179cb99750c@intel.com/

Mainly, x86 maintainers prefer imperative tone and references such as
"previous commit" can be confusing sometimes.


> Adjust USER_PTR_MAX if LAM enabled, allowing tag bits to be set for
> userspace pointers. The value for the constant is defined in a way to
> avoid overflow compiler warning on 32-bit config.
> 
> [1] https://download.vusec.net/papers/slam_sp24.pdf
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> ---
>  arch/x86/Kconfig             | 1 -
>  arch/x86/kernel/cpu/common.c | 5 +----
>  2 files changed, 1 insertion(+), 5 deletions(-)
>