A previous change ("KVM: PPC: Book3S HV: Add preempt_disable() around
virtual-mode HPTE bit-lock users") at [1] added preempt_disable() around
guest vCPU HPT hcalls and page fault handlers executed in virtual mode.
This ensures vCPU threads cannot be preempted while holding
HPTE_V_HVLOCK or the reverse-map lock.However, several host-side virtual-mode paths in book3s_64_mmu_hv.c also acquire HPTE_V_HVLOCK and lock_rmap() in process context with preemption enabled. Specifically, kvm_unmap_rmapp() and kvm_age_rmapp() take both locks during MMU notifier callbacks and memslot flushes, while resize_hpt_rehash_hpte() acquires HPTE_V_HVLOCK during HPT resizing. If a host thread is preempted while holding either bit-lock, any guest vCPU thread scheduled on the same CPU spinning for the same lock with preemption disabled will never yield, resulting in a permanent CPU hang. Fix this by disabling preemption across these host-side critical sections. For kvm_unmap_rmapp() and kvm_age_rmapp(), place preempt_disable() before lock_rmap() so that both the rmap chain lock and the subsequent HPTE_V_HVLOCK bit-lock are held under a single non-preemptible window. To preserve the ABBA lock ordering between the two locks, re-enable preemption after dropping the rmap lock on any retry or early-exit path before spinning on cpu_relax(), allowing the lock holder to be scheduled. For kvm_htab_write(), the HPT migration restore path, replace the direct calls to kvmppc_do_h_remove() with kvmppc_virtmode_do_h_remove(), a thin wrapper that brackets kvmppc_do_h_remove() with preempt_disable() and preempt_enable(), mirroring the existing kvmppc_virtmode_do_h_enter() helper. For resize_hpt_rehash_hpte(), place preempt_disable() before the try_lock_hpte() spin loop and preempt_enable() after unlock_hpte() at the function exit. [1] https://git.kernel.org/powerpc/c/abbbe5ff83e7c9ed3a4d61b73011f1df7bf87907 Fixes: 6165d5dd99db ("KVM: PPC: Book3S HV: add virtual mode handlers for HPT hcalls and page faults") Cc: [email protected] # v5.14+ Signed-off-by: Amit Machhiwal <[email protected]> --- Changes in this version: - Separated host-side fixes in book3s_64_mmu_hv.c into a standalone patch (guest-side paths were merged from v1 resend). - Previous discussion: https://lore.kernel.org/all/[email protected]/ arch/powerpc/kvm/book3s_64_mmu_hv.c | 33 +++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c index 2ccb3d138f46..8d85ce3440ae 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -47,6 +47,9 @@ static long kvmppc_virtmode_do_h_enter(struct kvm *kvm, unsigned long flags, long pte_index, unsigned long pteh, unsigned long ptel, unsigned long *pte_idx_ret); +static void kvmppc_virtmode_do_h_remove(struct kvm *kvm, unsigned long flags, + unsigned long pte_index, unsigned long avpn, + unsigned long *hpret); struct kvm_resize_hpt { /* These fields read-only after init */ @@ -308,6 +311,22 @@ static long kvmppc_virtmode_do_h_enter(struct kvm *kvm, unsigned long flags, } +/* + * Virtual-mode H_REMOVE. kvmppc_do_h_remove() is also called from real mode, + * where preempt_disable() is not usable, so the guard stays here. The function + * spins on HPTE_V_HVLOCK and then lock_rmap() (via remove_revmap_chain()); + * preemption must be disabled across both bit-locks so that spinning callers + * holding preempt_disable() can make forward progress. + */ +static void kvmppc_virtmode_do_h_remove(struct kvm *kvm, unsigned long flags, + unsigned long pte_index, unsigned long avpn, + unsigned long *hpret) +{ + preempt_disable(); + kvmppc_do_h_remove(kvm, flags, pte_index, avpn, hpret); + preempt_enable(); +} + static struct kvmppc_slb *kvmppc_mmu_book3s_hv_find_slbe(struct kvm_vcpu *vcpu, gva_t eaddr) { @@ -810,9 +829,11 @@ static void kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, rmapp = &memslot->arch.rmap[gfn - memslot->base_gfn]; for (;;) { + preempt_disable(); lock_rmap(rmapp); if (!(*rmapp & KVMPPC_RMAP_PRESENT)) { unlock_rmap(rmapp); + preempt_enable(); break; } @@ -826,6 +847,7 @@ static void kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, if (!try_lock_hpte(hptep, HPTE_V_HVLOCK)) { /* unlock rmap before spinning on the HPTE lock */ unlock_rmap(rmapp); + preempt_enable(); while (be64_to_cpu(hptep[0]) & HPTE_V_HVLOCK) cpu_relax(); continue; @@ -834,6 +856,7 @@ static void kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, kvmppc_unmap_hpte(kvm, i, memslot, rmapp, gfn); unlock_rmap(rmapp); __unlock_hpte(hptep, be64_to_cpu(hptep[0])); + preempt_enable(); } } @@ -890,6 +913,7 @@ static bool kvm_age_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, rmapp = &memslot->arch.rmap[gfn - memslot->base_gfn]; retry: + preempt_disable(); lock_rmap(rmapp); if (*rmapp & KVMPPC_RMAP_REFERENCED) { *rmapp &= ~KVMPPC_RMAP_REFERENCED; @@ -897,6 +921,7 @@ static bool kvm_age_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, } if (!(*rmapp & KVMPPC_RMAP_PRESENT)) { unlock_rmap(rmapp); + preempt_enable(); return ret; } @@ -912,6 +937,7 @@ static bool kvm_age_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, if (!try_lock_hpte(hptep, HPTE_V_HVLOCK)) { /* unlock rmap before spinning on the HPTE lock */ unlock_rmap(rmapp); + preempt_enable(); while (be64_to_cpu(hptep[0]) & HPTE_V_HVLOCK) cpu_relax(); goto retry; @@ -931,6 +957,7 @@ static bool kvm_age_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot, } while ((i = j) != head); unlock_rmap(rmapp); + preempt_enable(); return ret; } @@ -1219,6 +1246,7 @@ static unsigned long resize_hpt_rehash_hpte(struct kvm_resize_hpt *resize, if (!(vpte & HPTE_V_VALID) && !(vpte & HPTE_V_ABSENT)) return 0; /* nothing to do */ + preempt_disable(); while (!try_lock_hpte(hptep, HPTE_V_HVLOCK)) cpu_relax(); @@ -1346,6 +1374,7 @@ static unsigned long resize_hpt_rehash_hpte(struct kvm_resize_hpt *resize, out: unlock_hpte(hptep, vpte); + preempt_enable(); return ret; } @@ -1868,7 +1897,7 @@ static ssize_t kvm_htab_write(struct file *file, const char __user *buf, nb += HPTE_SIZE; if (be64_to_cpu(hptp[0]) & (HPTE_V_VALID | HPTE_V_ABSENT)) - kvmppc_do_h_remove(kvm, 0, i, 0, tmp); + kvmppc_virtmode_do_h_remove(kvm, 0, i, 0, tmp); err = -EIO; ret = kvmppc_virtmode_do_h_enter(kvm, H_EXACT, i, v, r, tmp); @@ -1897,7 +1926,7 @@ static ssize_t kvm_htab_write(struct file *file, const char __user *buf, for (j = 0; j < hdr.n_invalid; ++j) { if (be64_to_cpu(hptp[0]) & (HPTE_V_VALID | HPTE_V_ABSENT)) - kvmppc_do_h_remove(kvm, 0, i, 0, tmp); + kvmppc_virtmode_do_h_remove(kvm, 0, i, 0, tmp); ++i; hptp += 2; } base-commit: 129f5d395fd66b6587a5ac156b232cca060d6512 -- 2.54.0 (Apple Git-157)
