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authorPaul Mackerras <paulus@samba.org>2014-03-25 10:47:06 +1100
committerPaul Mackerras <paulus@samba.org>2014-03-29 19:58:35 +1100
commit797f9c07eb4cbc2d0ff27fac165a0b885da38840 (patch)
treeca135c3f5a5b2f37c702e69b55352b766764d4a6 /arch/powerpc/include/asm
parent739e2425fea6349ac674e93648953b3a08985f2f (diff)
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>
Diffstat (limited to 'arch/powerpc/include/asm')
-rw-r--r--arch/powerpc/include/asm/kvm_book3s_64.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index bf0fa8b0a883..51388befeddb 100644
--- 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__ */