[PATCH v2 09/15] KVM: arm64: nv: Ensure correct VL is loaded before saving SVE state

Oliver Upton
2024-06-13T20:18:47Z

It is possible that the guest hypervisor has selected a smaller VL than
the maximum for its nested guest. As such, ZCR_EL2 may be configured for
a different VL when exiting a nested guest.

Set ZCR_EL2 (via the EL1 alias) to the maximum VL for the VM before
saving SVE state as the SVE save area is dimensioned by the max VL.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/kvm/fpsimd.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 53168bbea8a7..bb2ef3166c63 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -193,11 +193,14 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
* Note that this means that at guest exit ZCR_EL1 is
* not necessarily the same as on guest entry.
*
- * Restoring the VL isn't needed in VHE mode since
- * ZCR_EL2 (accessed via ZCR_EL1) would fulfill the same
- * role when doing the save from EL2.
+ * ZCR_EL2 holds the guest hypervisor's VL when running
+ * a nested guest, which could be smaller than the
+ * max for the vCPU. Similar to above, we first need to
+ * switch to a VL consistent with the layout of the
+ * vCPU's SVE state. KVM support for NV implies VHE, so
+ * using the ZCR_EL1 alias is safe.
*/
- if (!has_vhe())
+ if (!has_vhe() || (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu)))
sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
SYS_ZCR_EL1);
}
--
2.45.2.627.g7a2c4fd464-goog