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[v3,07/15] KVM: arm64: nv: Ensure correct VL is loaded before saving SVE state

Message ID 20240620164653.1130714-8-oliver.upton@linux.dev (mailing list archive)
State New, archived
Headers show
Series KVM: arm64: nv: FPSIMD/SVE, plus some other CPTR goodies | expand

Commit Message

Oliver Upton June 20, 2024, 4:46 p.m. UTC 
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.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/fpsimd.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index d948f1c684ca..947486a111e1 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -190,11 +190,14 @@  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);
 		}