Re: [PATCH v4 8/9] KVM: TDX: Enable Bus Lock VM exit

[Nikolay Borisov]

On 8/19/26 12:49, Xiaoyao Li wrote:
> Enable Bus Lock VM exit functionality for TDX guests.
>
> Bus Lock VM exit is an existing feature supported by KVM.  Userspace can
> enable Bus Lock VM exit through KVM_BUS_LOCK_DETECTION_EXIT when it's
> reported as supported.  However, KVM reports the support of this CAP
> just based on the hardware capability but doesn't differentiate between
> VMX and TDX.  This leads to the issue that userspace can enable this cap
> for TDX guests without getting an error, but the feature is not actually
> enabled because KVM doesn't call the TDX module API to program the
> relevant TD VMCS fields.
>
> Enable Bus Lock VM exit for TDX guests by programming the
> BUS_LOCK_DETECTION control in the TD VMCS and by adding the exit handler.
>
> Note, there is no enumeration bit for this feature by TDX module because
> all TDX modules support it and allow to set the TD VMCS as long as the
> hardware supports the feature.
>
> Fixes: 161d34609f9b ("KVM: TDX: Make TDX VM type supported")
> Cc: stable@xxxxxxxxxxxxxxx
> Originally-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
> Changes in 4:
> - The code to make handle_bus_lock_vmexit() a shared helper is split
>    as a separate patch.
> - The handling for wait_for_sept_zap is no longer needed since a general
>    handling for it is added as a separate patch.
>
> Changes in v3:
> - Refine the changelog. (Rick)
>
> Changes in v2:
> - Don't overwrite the negative return value to 0. (Sashiko)
> - Clear the bus_lock_detected bit when it returns early for
>    wait_for_sept_zap case.
> - Add a note to clarify the feature is always supported by the TDX
>    module, to make Sashiko happy.

Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>