From: Greg Kurz groug@kaod.org
commit f54db39fbe40731c40aefdd3bc26e7d56d668c64 upstream.
Commit 062cfab7069f ("KVM: PPC: Book3S HV: XIVE: Make VP block size configurable") updated kvmppc_xive_vcpu_id_valid() in a way that allows userspace to trigger an assertion in skiboot and crash the host:
[ 696.186248988,3] XIVE[ IC 08 ] eq_blk != vp_blk (0 vs. 1) for target 0x4300008c/0 [ 696.186314757,0] Assert fail: hw/xive.c:2370:0 [ 696.186342458,0] Aborting! xive-kvCPU 0043 Backtrace: S: 0000000031e2b8f0 R: 0000000030013840 .backtrace+0x48 S: 0000000031e2b990 R: 000000003001b2d0 ._abort+0x4c S: 0000000031e2ba10 R: 000000003001b34c .assert_fail+0x34 S: 0000000031e2ba90 R: 0000000030058984 .xive_eq_for_target.part.20+0xb0 S: 0000000031e2bb40 R: 0000000030059fdc .xive_setup_silent_gather+0x2c S: 0000000031e2bc20 R: 000000003005a334 .opal_xive_set_vp_info+0x124 S: 0000000031e2bd20 R: 00000000300051a4 opal_entry+0x134 --- OPAL call token: 0x8a caller R1: 0xc000001f28563850 ---
XIVE maintains the interrupt context state of non-dispatched vCPUs in an internal VP structure. We allocate a bunch of those on startup to accommodate all possible vCPUs. Each VP has an id, that we derive from the vCPU id for efficiency:
static inline u32 kvmppc_xive_vp(struct kvmppc_xive *xive, u32 server) { return xive->vp_base + kvmppc_pack_vcpu_id(xive->kvm, server); }
The KVM XIVE device used to allocate KVM_MAX_VCPUS VPs. This was limitting the number of concurrent VMs because the VP space is limited on the HW. Since most of the time, VMs run with a lot less vCPUs, commit 062cfab7069f ("KVM: PPC: Book3S HV: XIVE: Make VP block size configurable") gave the possibility for userspace to tune the size of the VP block through the KVM_DEV_XIVE_NR_SERVERS attribute.
The check in kvmppc_pack_vcpu_id() was changed from
cpu < KVM_MAX_VCPUS * xive->kvm->arch.emul_smt_mode
to
cpu < xive->nr_servers * xive->kvm->arch.emul_smt_mode
The previous check was based on the fact that the VP block had KVM_MAX_VCPUS entries and that kvmppc_pack_vcpu_id() guarantees that packed vCPU ids are below KVM_MAX_VCPUS. We've changed the size of the VP block, but kvmppc_pack_vcpu_id() has nothing to do with it and it certainly doesn't ensure that the packed vCPU ids are below xive->nr_servers. kvmppc_xive_vcpu_id_valid() might thus return true when the VM was configured with a non-standard VSMT mode, even if the packed vCPU id is higher than what we expect. We end up using an unallocated VP id, which confuses OPAL. The assert in OPAL is probably abusive and should be converted to a regular error that the kernel can handle, but we shouldn't really use broken VP ids in the first place.
Fix kvmppc_xive_vcpu_id_valid() so that it checks the packed vCPU id is below xive->nr_servers, which is explicitly what we want.
Fixes: 062cfab7069f ("KVM: PPC: Book3S HV: XIVE: Make VP block size configurable") Cc: stable@vger.kernel.org # v5.5+ Signed-off-by: Greg Kurz groug@kaod.org Reviewed-by: Cédric Le Goater clg@kaod.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/160673876747.695514.1809676603724514920.stgit@bahi... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kvm/book3s_xive.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
--- a/arch/powerpc/kvm/book3s_xive.c +++ b/arch/powerpc/kvm/book3s_xive.c @@ -1214,12 +1214,9 @@ void kvmppc_xive_cleanup_vcpu(struct kvm static bool kvmppc_xive_vcpu_id_valid(struct kvmppc_xive *xive, u32 cpu) { /* We have a block of xive->nr_servers VPs. We just need to check - * raw vCPU ids are below the expected limit for this guest's - * core stride ; kvmppc_pack_vcpu_id() will pack them down to an - * index that can be safely used to compute a VP id that belongs - * to the VP block. + * packed vCPU ids are below that. */ - return cpu < xive->nr_servers * xive->kvm->arch.emul_smt_mode; + return kvmppc_pack_vcpu_id(xive->kvm, cpu) < xive->nr_servers; }
int kvmppc_xive_compute_vp_id(struct kvmppc_xive *xive, u32 cpu, u32 *vp)