On Thu, 12 Dec 2024 15:14:06 +0000,
Joey Gouly <joey.gouly@xxxxxxx> wrote:
>
> From: James Morse <james.morse@xxxxxxx>
>
> commit 6685f5d572c22e1003e7c0d089afe1c64340ab1f upstream.
>
> commit 011e5f5bf529f ("arm64/cpufeature: Add remaining feature bits in
> ID_AA64PFR0 register") exposed the MPAM field of AA64PFR0_EL1 to guests,
> but didn't add trap handling. A previous patch supplied the missing trap
> handling.
>
> Existing VMs that have the MPAM field of ID_AA64PFR0_EL1 set need to
> be migratable, but there is little point enabling the MPAM CPU
> interface on new VMs until there is something a guest can do with it.
>
> Clear the MPAM field from the guest's ID_AA64PFR0_EL1 and on hardware
> that supports MPAM, politely ignore the VMMs attempts to set this bit.
>
> Guests exposed to this bug have the sanitised value of the MPAM field,
> so only the correct value needs to be ignored. This means the field
> can continue to be used to block migration to incompatible hardware
> (between MPAM=1 and MPAM=5), and the VMM can't rely on the field
> being ignored.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Co-developed-by: Joey Gouly <joey.gouly@xxxxxxx>
> Signed-off-by: Joey Gouly <joey.gouly@xxxxxxx>
> Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20241030160317.2528209-7-joey.gouly@xxxxxxx
> Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> [ joey: fixed up merge conflict, no ID_FILTERED macro in 6.6 ]
> Signed-off-by: Joey Gouly <joey.gouly@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 6.6.x
> Cc: Vitaly Chikunov <vt@xxxxxxxxxxxx>
> Link: https://lore.kernel.org/linux-arm-kernel/20241202045830.e4yy3nkvxtzaybxk@xxxxxxxxxxxx/
Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
M.
--
Without deviation from the norm, progress is not possible.
