From: David Woodhouse In order to preserve guest compatibility across kernel upgrades, allow userspace to select GICD_IIDR revision 1. This allows compatibility with the original behaviour from before commit d53c2c29ae0d ("KVM: arm/arm64: vgic: Allow configuration of interrupt groups") where interrupt groups are not guest-configurable. When revision 1 is selected: - GICv2: IGROUPR reads as zero (group 0), writes are ignored - GICv3: IGROUPR reads as all-ones (group 1), writes are ignored - v2_groups_user_writable is not set This is implemented by checking the implementation revision in vgic_mmio_write_group() and suppressing writes when the revision is below 2. The read side needs no change since the per-IRQ group reset values already match the expected behaviour. For GICv2, commit 32f8777ed92d7 ("KVM: arm/arm64: vgic: Let userspace opt-in to writable v2 IGROUPR") introduced a confusing model where IGROUPR registers were not writable from userspace by default until the IIDR was written — even if it was written to the *same* as its default value (which, in fact, was the only thing that userspace *could* set it to before commit a0e6ae45af17 fixed the IIDR write path). Furthermore, even when the v2_groups_user_writable flag wasn't set, the *guest* could still actually write to the registers... but userspace couldn't save/restore them. That default behaviour for GICv2 remains unchanged; it can be fixed in a future commit. Fixes: d53c2c29ae0d ("KVM: arm/arm64: vgic: Allow configuration of interrupt groups") Signed-off-by: David Woodhouse --- arch/arm64/kvm/vgic/vgic-mmio-v2.c | 3 +++ arch/arm64/kvm/vgic/vgic-mmio-v3.c | 4 ++++ arch/arm64/kvm/vgic/vgic-mmio.c | 4 ++++ include/kvm/arm_vgic.h | 1 + 4 files changed, 12 insertions(+) diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v2.c b/arch/arm64/kvm/vgic/vgic-mmio-v2.c index 0643e333db35..e5714f7fd2ec 100644 --- a/arch/arm64/kvm/vgic/vgic-mmio-v2.c +++ b/arch/arm64/kvm/vgic/vgic-mmio-v2.c @@ -20,6 +20,7 @@ * Revision 1: Report GICv2 interrupts as group 0 instead of group 1 * Revision 2: Interrupt groups are guest-configurable and signaled using * their configured groups. + * Revision 3: GICv2 behaviour is unchanged from revision 2. */ static unsigned long vgic_mmio_read_v2_misc(struct kvm_vcpu *vcpu, @@ -96,6 +97,8 @@ static int vgic_mmio_uaccess_write_v2_misc(struct kvm_vcpu *vcpu, case KVM_VGIC_IMP_REV_2: case KVM_VGIC_IMP_REV_3: vcpu->kvm->arch.vgic.v2_groups_user_writable = true; + fallthrough; + case KVM_VGIC_IMP_REV_1: dist->implementation_rev = reg; return 0; default: diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c index 5913a20d8301..0130db71cfc9 100644 --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c @@ -74,8 +74,11 @@ bool vgic_supports_direct_sgis(struct kvm *kvm) /* * The Revision field in the IIDR have the following meanings: * + * Revision 1: Interrupt groups are not guest-configurable. + * IGROUPR reads as all-ones (group 1), writes ignored. * Revision 2: Interrupt groups are guest-configurable and signaled using * their configured groups. + * Revision 3: GICR_CTLR.{IR,CES} are advertised. */ static unsigned long vgic_mmio_read_v3_misc(struct kvm_vcpu *vcpu, @@ -196,6 +199,7 @@ static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu, reg = FIELD_GET(GICD_IIDR_REVISION_MASK, val); switch (reg) { + case KVM_VGIC_IMP_REV_1: case KVM_VGIC_IMP_REV_2: case KVM_VGIC_IMP_REV_3: dist->implementation_rev = reg; diff --git a/arch/arm64/kvm/vgic/vgic-mmio.c b/arch/arm64/kvm/vgic/vgic-mmio.c index 74d76dec9730..1b662744ec5b 100644 --- a/arch/arm64/kvm/vgic/vgic-mmio.c +++ b/arch/arm64/kvm/vgic/vgic-mmio.c @@ -73,6 +73,10 @@ void vgic_mmio_write_group(struct kvm_vcpu *vcpu, gpa_t addr, int i; unsigned long flags; + /* Revision 1 and below: groups are not guest-configurable. */ + if (vgic_get_implementation_rev(vcpu) < KVM_VGIC_IMP_REV_2) + return; + for (i = 0; i < len * 8; i++) { struct vgic_irq *irq = vgic_get_vcpu_irq(vcpu, intid + i); diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h index 1388dc6028a9..16811ec03d54 100644 --- a/include/kvm/arm_vgic.h +++ b/include/kvm/arm_vgic.h @@ -372,6 +372,7 @@ struct vgic_dist { /* Implementation revision as reported in the GICD_IIDR */ u32 implementation_rev; +#define KVM_VGIC_IMP_REV_1 1 /* GICv2 interrupts as group 0 */ #define KVM_VGIC_IMP_REV_2 2 /* GICv2 restorable groups */ #define KVM_VGIC_IMP_REV_3 3 /* GICv3 GICR_CTLR.{IW,CES,RWP} */ #define KVM_VGIC_IMP_REV_LATEST KVM_VGIC_IMP_REV_3 -- 2.51.0