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Re: [PATCH 13/22] x86: FRED enumerations
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 18 Aug 2025 11:02:11 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 18 Aug 2025 09:02:16 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.08.2025 22:23, Andrew Cooper wrote:
> Of note, CR4.FRED is bit 32 and cannot enabled outside of 64bit mode.
>
> Most supported toolchains don't understand the FRED instructions yet. ERETU
> and ERETS are easy to wrap (they encoded as REPZ/REPNE CLAC), while LKGS is
> more complicated and deferred for now.
>
> I have intentionally named the FRED MSRs differently to the spec. In the
> spec, the stack pointer names alias the TSS fields of the same name, despite
> very different semantics.
Hmm, looking at this again I'm not entirely convinced: Staying in sync with
the spec also has its merits, and the FRED infix is sufficiently distinguishing
imo.
Jan
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