diff options
Diffstat (limited to 'arch/powerpc/include/asm/kvm_book3s.h')
| -rw-r--r-- | arch/powerpc/include/asm/kvm_book3s.h | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h index 1f345a0b6ba2..83a9aa3cf689 100644 --- a/arch/powerpc/include/asm/kvm_book3s.h +++ b/arch/powerpc/include/asm/kvm_book3s.h @@ -390,4 +390,51 @@ extern int kvmppc_h_logical_ci_store(struct kvm_vcpu *vcpu); #define SPLIT_HACK_MASK 0xff000000 #define SPLIT_HACK_OFFS 0xfb000000 +/* + * This packs a VCPU ID from the [0..KVM_MAX_VCPU_ID) space down to the + * [0..KVM_MAX_VCPUS) space, using knowledge of the guest's core stride + * (but not its actual threading mode, which is not available) to avoid + * collisions. + * + * The implementation leaves VCPU IDs from the range [0..KVM_MAX_VCPUS) (block + * 0) unchanged: if the guest is filling each VCORE completely then it will be + * using consecutive IDs and it will fill the space without any packing. + * + * For higher VCPU IDs, the packed ID is based on the VCPU ID modulo + * KVM_MAX_VCPUS (effectively masking off the top bits) and then an offset is + * added to avoid collisions. + * + * VCPU IDs in the range [KVM_MAX_VCPUS..(KVM_MAX_VCPUS*2)) (block 1) are only + * possible if the guest is leaving at least 1/2 of each VCORE empty, so IDs + * can be safely packed into the second half of each VCORE by adding an offset + * of (stride / 2). + * + * Similarly, if VCPU IDs in the range [(KVM_MAX_VCPUS*2)..(KVM_MAX_VCPUS*4)) + * (blocks 2 and 3) are seen, the guest must be leaving at least 3/4 of each + * VCORE empty so packed IDs can be offset by (stride / 4) and (stride * 3 / 4). + * + * Finally, VCPU IDs from blocks 5..7 will only be seen if the guest is using a + * stride of 8 and 1 thread per core so the remaining offsets of 1, 5, 3 and 7 + * must be free to use. + * + * (The offsets for each block are stored in block_offsets[], indexed by the + * block number if the stride is 8. For cases where the guest's stride is less + * than 8, we can re-use the block_offsets array by multiplying the block + * number by (MAX_SMT_THREADS / stride) to reach the correct entry.) + */ +static inline u32 kvmppc_pack_vcpu_id(struct kvm *kvm, u32 id) +{ + const int block_offsets[MAX_SMT_THREADS] = {0, 4, 2, 6, 1, 5, 3, 7}; + int stride = kvm->arch.emul_smt_mode; + int block = (id / KVM_MAX_VCPUS) * (MAX_SMT_THREADS / stride); + u32 packed_id; + + if (WARN_ONCE(block >= MAX_SMT_THREADS, "VCPU ID too large to pack")) + return 0; + packed_id = (id % KVM_MAX_VCPUS) + block_offsets[block]; + if (WARN_ONCE(packed_id >= KVM_MAX_VCPUS, "VCPU ID packing failed")) + return 0; + return packed_id; +} + #endif /* __ASM_KVM_BOOK3S_H__ */ |