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Re: [PATCH v2 4/8] x86: Initial support for WRMSRNS
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 12 Jan 2023 16:11:13 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 12 Jan 2023 15:11:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.01.2023 14:58, Andrew Cooper wrote:
> On 12/01/2023 12:58 pm, Jan Beulich wrote:
>> Do you have any indications towards a CS prefix being the least risky
>> one to use here (or in general)?
>
> Yes.
>
> Remember it's the prefix recommended for, and used by,
> -mbranches-within-32B-boundaries to work around the Skylake jmp errata.
>
> And based on this justification, its also the prefix we use for padding
> on various jmp/call's for retpoline inlining purposes.
While I'm okay with the reply, I'd like to point out that in those cases
address or operand size prefix simply could not have been used, for the
insns in question having explicit operands which would be affected. Which
is unlike the case here.
Jan
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