On Fri, 8 Jan 2021 at 18:12, Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> It looks like we have broken firmware out there that wrongly advertises
> a GICv2 compatibility interface, despite the CPUs not being able to deal
> with it.
>
> To work around this, check that the CPU initialising KVM is actually able
> to switch to MMIO instead of system registers, and use that as a
> precondition to enable GICv2 compatibility in KVM.
>
> Note that the detection happens on a single CPU. If the firmware is
> lying *and* that the CPUs are asymetric, all hope is lost anyway.
>
> Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/kvm/hyp/vgic-v3-sr.c | 34 +++++++++++++++++++++++++++++++--
> arch/arm64/kvm/vgic/vgic-v3.c | 8 ++++++--
> 2 files changed, 38 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> index 005daa0c9dd7..d504499ab917 100644
> --- a/arch/arm64/kvm/hyp/vgic-v3-sr.c
> +++ b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> @@ -408,11 +408,41 @@ void __vgic_v3_init_lrs(void)
> /*
> * Return the GIC CPU configuration:
> * - [31:0] ICH_VTR_EL2
> - * - [63:32] RES0
> + * - [62:32] RES0
> + * - [63] MMIO (GICv2) capable
> */
> u64 __vgic_v3_get_gic_config(void)
> {
> - return read_gicreg(ICH_VTR_EL2);
> + u64 sre = read_gicreg(ICC_SRE_EL1);
> + unsigned long flags = 0;
> + bool v2_capable;
> +
> + /*
> + * To check whether we have a MMIO-based (GICv2 compatible)
> + * CPU interface, we need to disable the system register
> + * view. To do that safely, we have to prevent any interrupt
> + * from firing (which would be deadly).
> + *
> + * Note that this only makes sense on VHE, as interrupts are
> + * already masked for nVHE as part of the exception entry to
> + * EL2.
> + */
> + if (has_vhe())
> + flags = local_daif_save();
> +
> + write_gicreg(0, ICC_SRE_EL1);
> + isb();
> +
> + v2_capable = !(read_gicreg(ICC_SRE_EL1) & ICC_SRE_EL1_SRE);
> +
> + write_gicreg(sre, ICC_SRE_EL1);
> + isb();
> +
> + if (has_vhe())
> + local_daif_restore(flags);
> +
> + return (read_gicreg(ICH_VTR_EL2) |
> + v2_capable ? (1ULL << 63) : 0);
> }
>
Is it necessary to perform this check unconditionally? We only care
about this if the firmware claims v2 compat support.
> u64 __vgic_v3_read_vmcr(void)
> diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
> index 8e7bf3151057..67b27b47312b 100644
> --- a/arch/arm64/kvm/vgic/vgic-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-v3.c
> @@ -584,8 +584,10 @@ early_param("kvm-arm.vgic_v4_enable", early_gicv4_enable);
> int vgic_v3_probe(const struct gic_kvm_info *info)
> {
> u64 ich_vtr_el2 = kvm_call_hyp_ret(__vgic_v3_get_gic_config);
> + bool has_v2;
> int ret;
>
> + has_v2 = ich_vtr_el2 >> 63;
> ich_vtr_el2 = (u32)ich_vtr_el2;
>
> /*
> @@ -605,13 +607,15 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
> gicv4_enable ? "en" : "dis");
> }
>
> + kvm_vgic_global_state.vcpu_base = 0;
> +
> if (!info->vcpu.start) {
> kvm_info("GICv3: no GICV resource entry\n");
> - kvm_vgic_global_state.vcpu_base = 0;
> + } else if (!has_v2) {
> + pr_warn("CPU interface incapable of MMIO access\n");
> } else if (!PAGE_ALIGNED(info->vcpu.start)) {
> pr_warn("GICV physical address 0x%llx not page aligned\n",
> (unsigned long long)info->vcpu.start);
> - kvm_vgic_global_state.vcpu_base = 0;
> } else {
> kvm_vgic_global_state.vcpu_base = info->vcpu.start;
> kvm_vgic_global_state.can_emulate_gicv2 = true;
> --
> 2.29.2
>
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