[PATCH v4 11/41] KVM: arm64: Force guest EL1 to use user-space's partid configuration

Ben Horgan
2026-02-03T21:45:04Z

From: James Morse <james.morse@arm.com>

While we trap the guest's attempts to read/write the MPAM control
registers, the hardware continues to use them. Guest-EL0 uses KVM's
user-space's configuration, as the value is left in the register, and
guest-EL1 uses either the host kernel's configuration, or in the case of
VHE, the UNKNOWN reset value of MPAM1_EL1.

We want to force the guest-EL1 to use KVM's user-space's MPAM
configuration. On nVHE rely on MPAM0_EL1 and MPAM1_EL1 always being
programmed the same and on VHE copy MPAM0_EL1 into the guest's
MPAM1_EL1. There is no need to restore as this is out of context once TGE
is set.

Tested-by: Gavin Shan <gshan@redhat.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since rfc:
Drop the unneeded __mpam_guest_load() in nvhre and the MPAM1_EL1 save restore
Defer EL2 handling until next patch

Changes since v2:
Use mask (Oliver)
---
arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kvm/hyp/vhe/sysreg-sr.c b/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
index f28c6cf4fe1b..9fb8e6628611 100644
--- a/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
@@ -183,6 +183,18 @@ void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt)
}
NOKPROBE_SYMBOL(sysreg_restore_guest_state_vhe);

+/*
+ * The _EL0 value was written by the host's context switch and belongs to the
+ * VMM. Copy this into the guest's _EL1 register.
+ */
+static inline void __mpam_guest_load(void)
+{
+ u64 mask = MPAM0_EL1_PARTID_D | MPAM0_EL1_PARTID_I | MPAM0_EL1_PMG_D | MPAM0_EL1_PMG_I;
+
+ if (system_supports_mpam())
+ write_sysreg_el1(read_sysreg_s(SYS_MPAM0_EL1) & mask, SYS_MPAM1);
+}
+
/**
* __vcpu_load_switch_sysregs - Load guest system registers to the physical CPU
*
@@ -222,6 +234,7 @@ void __vcpu_load_switch_sysregs(struct kvm_vcpu *vcpu)
*/
__sysreg32_restore_state(vcpu);
__sysreg_restore_user_state(guest_ctxt);
+ __mpam_guest_load();

if (unlikely(is_hyp_ctxt(vcpu))) {
__sysreg_restore_vel2_state(vcpu);
--
2.43.0