[PATCH] KVM: arm64: Fix CPU interface MMIO compatibility detection

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Marc Zyngier [mailto:maz at kernel.org]
> Sent: 23 March 2021 16:23
> To: kvmarm at lists.cs.columbia.edu; kvm at vger.kernel.org;
> linux-arm-kernel at lists.infradead.org
> Cc: Ard Biesheuvel <ardb at kernel.org>; kernel-team at android.com; Shameerali
> Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>
> Subject: [PATCH] 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 on HiSilicon D06 platform where the original issue(firmware wrongly
advertising GICv2-on-v3 compatibility) was reported and all seems to be fine.

Though not sure whether this fix is relevant to this particular platform,
FWIW,

  Tested-by: Shameer Kolothum <shameerali.kolothum.thodi at huawei.com>

Thanks,
Shameer

> Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>
> Fixes: 9739f6ef053f ("KVM: arm64: Workaround firmware wrongly advertising
> GICv2-on-v3 compatibility")
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/vgic-v3-sr.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c
> b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> index ee3682b9873c..39f8f7f9227c 100644
> --- 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);
> --
> 2.30.0