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Re: [PATCH for-4.22] x86/fred: Enable FRED by default on AMD systems
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 3 Jun 2026 08:27:11 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 03 Jun 2026 06:27:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.06.2026 18:45, Andrew Cooper wrote:
> FRED is now believed to be complete for AMD systems, and has had its tyres
> kicked by both XenServer and AMD. Enable FRED by default on capable AMD
> systems (Zen6 and later).
>
> Support on Intel is still not yet complete. Leave it as tech preview and not
> security supported.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with one remark:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -1259,12 +1259,12 @@ does not provide `VM_ENTRY_LOAD_GUEST_PAT`.
> ### fred (x86)
> > `= <bool>`
>
> -> Default: `false`
> +> Default: `true` on AMD, `false` otherwise
>
> Flexible Return and Event Delivery is an overhaul of interrupt, exception and
> system call handling, fixing many corner cases in the x86 architecture, and
> -expected in hardware from 2025. Support in Xen is a work in progress and
> -disabled by default.
> +expected in hardware from 2026. FRED is fully supported on AMD hardware.
> +Intel hardware is still tech preview and not security supported.
Is having "security" here really appropriate? There's a functional issue to be
sorted. That's expressed by "tech preview", yes, but it still feels somewhat
odd. If you want to keep the word, may I suggest to insert "in particular"?
May I further suggest "On Intel hardware it is ..."?
Jan
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