KVM: PPC: Book3S HV: Don't use kvm_memslots() in real mode

With HV KVM, some high-frequency hypercalls such as H_ENTER are handled
in real mode, and need to access the memslots array for the guest.
Accessing the memslots array is safe, because we hold the SRCU read
lock for the whole time that a guest vcpu is running.  However, the
checks that kvm_memslots() does when lockdep is enabled are potentially
unsafe in real mode, when only the linear mapping is available.
Furthermore, kvm_memslots() can be called from a secondary CPU thread,
which is an offline CPU from the point of view of the host kernel,
and is not running the task which holds the SRCU read lock.

To avoid false positives in the checks in kvm_memslots(), and to avoid
possible side effects from doing the checks in real mode, this replaces
kvm_memslots() with kvm_memslots_raw() in all the places that execute
in real mode.  kvm_memslots_raw() is a new function that is like
kvm_memslots() but uses rcu_dereference_raw_notrace() instead of
kvm_dereference_check().

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Scott Wood <scottwood@freescale.com>

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index bf0fa8b0a883f8ecac068d0b9376ec6e45a2de05..51388befeddb37d454e33ab10cb196e2930f93fb 100644 (file)
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -289,6 +289,18 @@ static inline void note_hpte_modification(struct kvm *kvm,
        if (atomic_read(&kvm->arch.hpte_mod_interest))
                rev->guest_rpte |= HPTE_GR_MODIFIED;
 }
+
+/*
+ * Like kvm_memslots(), but for use in real mode when we can't do
+ * any RCU stuff (since the secondary threads are offline from the
+ * kernel's point of view), and we can't print anything.
+ * Thus we use rcu_dereference_raw() rather than rcu_dereference_check().
+ */
+static inline struct kvm_memslots *kvm_memslots_raw(struct kvm *kvm)
+{
+       return rcu_dereference_raw_notrace(kvm->memslots);
+}
+
 #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
 
 #endif /* __ASM_KVM_BOOK3S_64_H__ */

diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 37fb3caa4c80a59c5162b92943e1d7878991b8f1..1d6c56ad5b605f240770ed8ab6483f8b3fa00408 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -111,7 +111,7 @@ static void remove_revmap_chain(struct kvm *kvm, long pte_index,
        rcbits = hpte_r & (HPTE_R_R | HPTE_R_C);
        ptel = rev->guest_rpte |= rcbits;
        gfn = hpte_rpn(ptel, hpte_page_size(hpte_v, ptel));
-       memslot = __gfn_to_memslot(kvm_memslots(kvm), gfn);
+       memslot = __gfn_to_memslot(kvm_memslots_raw(kvm), gfn);
        if (!memslot)
                return;
 
@@ -192,7 +192,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
        /* Find the memslot (if any) for this address */
        gpa = (ptel & HPTE_R_RPN) & ~(psize - 1);
        gfn = gpa >> PAGE_SHIFT;
-       memslot = __gfn_to_memslot(kvm_memslots(kvm), gfn);
+       memslot = __gfn_to_memslot(kvm_memslots_raw(kvm), gfn);
        pa = 0;
        is_io = ~0ul;
        rmap = NULL;
@@ -670,7 +670,7 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags,
 
                        psize = hpte_page_size(v, r);
                        gfn = ((r & HPTE_R_RPN) & ~(psize - 1)) >> PAGE_SHIFT;
-                       memslot = __gfn_to_memslot(kvm_memslots(kvm), gfn);
+                       memslot = __gfn_to_memslot(kvm_memslots_raw(kvm), gfn);
                        if (memslot) {
                                hva = __gfn_to_hva_memslot(memslot, gfn);
                                pte = lookup_linux_pte_and_update(pgdir, hva,