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Re: [PATCH v3] x86/vmx: add support for virtualize SPEC_CTRL
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 19 Feb 2024 10:04:55 +0100
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- Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 19 Feb 2024 09:05:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.02.2024 17:46, Roger Pau Monne wrote:
> The feature is defined in the tertiary exec control, and is available starting
> from Sapphire Rapids and Alder Lake CPUs.
>
> When enabled, two extra VMCS fields are used: SPEC_CTRL mask and shadow. Bits
> set in mask are not allowed to be toggled by the guest (either set or clear)
> and the value in the shadow field is the value the guest expects to be in the
> SPEC_CTRL register.
>
> By using it the hypervisor can force the value of SPEC_CTRL bits behind the
> guest back without having to trap all accesses to SPEC_CTRL, note that no bits
> are forced into the guest as part of this patch. It also allows getting rid
> of
> SPEC_CTRL in the guest MSR load list, since the value in the shadow field will
> be loaded by the hardware on vmentry.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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