[PATCH] KVM: arm64: vgic-v3: Consistently populate ID_AA64PFR0_EL1.GIC

[PATCH] KVM: arm64: vgic-v3: Consistently populate ID_AA64PFR0_EL1.GIC

[Marc Zyngier]

When adding support for the slightly wonky Apple M1, we had to
populate ID_AA64PFR0_EL1.GIC==1 to present something to the guest,
as the HW itself doesn't advertise the feature.

However, we gated this on the in-kernel irqchip being created.
This causes some trouble for QEMU, which snapshots the state of
the registers before creating a virtual GIC, and then tries to
restore these registers once the GIC has been created.  Obviously,
between the two stages, ID_AA64PFR0_EL1.GIC has changed value,
and the write fails.

The fix is to actually emulate the HW, and always populate the
field if the HW is capable of it.

Fixes: 562e530fd770 ("KVM: arm64: Force ID_AA64PFR0_EL1.GIC=1 when exposing a virtual GICv3")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
---
 arch/arm64/kvm/sys_regs.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 7b45c040cc27..adf408c09cdb 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1123,8 +1123,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_CSV2), (u64)vcpu->kvm->arch.pfr0_csv2);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_CSV3);
 		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
-		if (irqchip_in_kernel(vcpu->kvm) &&
-		    vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
+		if (kvm_vgic_global_state.type == VGIC_V3) {
 			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_GIC);
 			val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_GIC), 1);
 		}
-- 
2.34.1


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Re: [PATCH] KVM: arm64: vgic-v3: Consistently populate ID_AA64PFR0_EL1.GIC

[Oliver Upton]

On Tue, May 03, 2022 at 10:14:24PM +0100, Marc Zyngier wrote:
> When adding support for the slightly wonky Apple M1, we had to
> populate ID_AA64PFR0_EL1.GIC==1 to present something to the guest,
> as the HW itself doesn't advertise the feature.
> 
> However, we gated this on the in-kernel irqchip being created.
> This causes some trouble for QEMU, which snapshots the state of
> the registers before creating a virtual GIC, and then tries to
> restore these registers once the GIC has been created.  Obviously,
> between the two stages, ID_AA64PFR0_EL1.GIC has changed value,
> and the write fails.
> 
> The fix is to actually emulate the HW, and always populate the
> field if the HW is capable of it.
> 
> Fixes: 562e530fd770 ("KVM: arm64: Force ID_AA64PFR0_EL1.GIC=1 when exposing a virtual GICv3")
> Cc: stable@vger.kernel.org
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Reported-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Oliver Upton <oupton@google.com>

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