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Re: [PATCH] x86/hvm: Configuration for Linear Address Space Separation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 30 Mar 2026 09:52:45 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 30 Mar 2026 07:52:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.03.2026 14:18, Andrew Cooper wrote:
> LASS is a feature designed in the aftermath of Meltdown, which codifies the
> user/kernel split in address space in order to block entire classes of
> sidechanels. Specifically, it allows the CPU to terminate any memory access
> into the wrong half of the address space based on linear address alone and
> without needing a pagewalk.
>
> It is available in CPUs starting with Intel Sapphire Rapids (2023).
>
> For now, allow LASS to be opted in to, but leave it off by default. Some work
> in the emulator is going to be needed to enable it by default.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Abdel is going to look into the emulator side of things, which is going to be
> easier with this patch already in place. I intend to get it fully supported
> for 4.22.
It indeed as "as simple as this" if you leave out the emulator part.
Jan
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