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Re: [PATCH v4] x86/HVM: support emulated UMIP
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 17 Mar 2023 16:01:59 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>
- Delivery-date: Fri, 17 Mar 2023 15:02:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.03.2023 15:29, Roger Pau Monné wrote:
> On Thu, Apr 15, 2021 at 11:47:42AM +0200, Jan Beulich wrote:
>> There are three noteworthy drawbacks:
>> 1) The intercepts we need to enable here are CPL-independent, i.e. we
>> now have to emulate certain instructions for ring 0.
>> 2) On VMX there's no intercept for SMSW, so the emulation isn't really
>> complete there.
>
> Then I'm afraid we can't set the bit in the max CPUID policy. What
> about domains being migrated from a host that has UMIP to an Intel
> host where UMIP is emulated? They would see a change in behavior in
> SMSW, and the behavior won't match the ISA anymore.
Right, but that's the price to pay if we want such emulation (which back
at the time did look at least desirable, because the other affected insns
are more important to deal with). Not setting the bit in the max policy
is as good as not having emulation on VMX at all then.
Jan
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