KVM: arm64: Fix CPU interface MMIO compatibility detection

In order to detect whether a GICv3 CPU interface is MMIO capable,
we switch ICC_SRE_EL1.SRE to 0 and check whether it sticks.

However, this is only possible if *ALL* of the HCR_EL2 interrupt
overrides are set, and the CPU is perfectly allowed to ignore
the write to ICC_SRE_EL1 otherwise. This leads KVM to pretend
that a whole bunch of ARMv8.0 CPUs aren't MMIO-capable, and
breaks VMs that should work correctly otherwise.

Fix this by setting IMO/FMO/IMO before touching ICC_SRE_EL1,
and clear them afterwards. This allows us to reliably detect
the CPU interface capabilities.

Tested-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Fixes: 9739f6ef053f ("KVM: arm64: Workaround firmware wrongly advertising GICv2-on-v3 compatibility")
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c b/arch/arm64/kvm/hyp/vgic-v3-sr.c
index ee3682b..39f8f7f 100644 (file)
--- a/arch/arm64/kvm/hyp/vgic-v3-sr.c
+++ b/arch/arm64/kvm/hyp/vgic-v3-sr.c
@@ -429,6 +429,13 @@ u64 __vgic_v3_get_gic_config(void)
        if (has_vhe())
                flags = local_daif_save();
 
+       /*
+        * Table 11-2 "Permitted ICC_SRE_ELx.SRE settings" indicates
+        * that to be able to set ICC_SRE_EL1.SRE to 0, all the
+        * interrupt overrides must be set. You've got to love this.
+        */
+       sysreg_clear_set(hcr_el2, 0, HCR_AMO | HCR_FMO | HCR_IMO);
+       isb();
        write_gicreg(0, ICC_SRE_EL1);
        isb();
 
@@ -436,6 +443,8 @@ u64 __vgic_v3_get_gic_config(void)
 
        write_gicreg(sre, ICC_SRE_EL1);
        isb();
+       sysreg_clear_set(hcr_el2, HCR_AMO | HCR_FMO | HCR_IMO, 0);
+       isb();
 
        if (has_vhe())
                local_daif_restore(flags);