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From: Lai Jiangshan on 19 Apr 2010 05:50
The RCU/SRCU API have already changed for proving RCU usage.

I got the following dmesg when PROVE_RCU=y because we used incorrect API.
This patch coverts rcu_deference() to srcu_dereference() or family API.

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
arch/x86/kvm/mmu.c:3020 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
2 locks held by qemu-system-x86/8550:
#0: (&kvm->slots_lock){+.+.+.}, at: [<ffffffffa011a6ac>] kvm_set_memory_region+0x29/0x50 [kvm]
#1: (&(&kvm->mmu_lock)->rlock){+.+...}, at: [<ffffffffa012262d>] kvm_arch_commit_memory_region+0xa6/0xe2 [kvm]

stack backtrace:
Pid: 8550, comm: qemu-system-x86 Not tainted 2.6.34-rc4-tip-01028-g939eab1 #27
Call Trace:
[<ffffffff8106c59e>] lockdep_rcu_dereference+0xaa/0xb3
[<ffffffffa012f6c1>] kvm_mmu_calculate_mmu_pages+0x44/0x7d [kvm]
[<ffffffffa012263e>] kvm_arch_commit_memory_region+0xb7/0xe2 [kvm]
[<ffffffffa011a5d7>] __kvm_set_memory_region+0x636/0x6e2 [kvm]
[<ffffffffa011a6ba>] kvm_set_memory_region+0x37/0x50 [kvm]
[<ffffffffa015e956>] vmx_set_tss_addr+0x46/0x5a [kvm_intel]
[<ffffffffa0126592>] kvm_arch_vm_ioctl+0x17a/0xcf8 [kvm]
[<ffffffff810a8692>] ? unlock_page+0x27/0x2c
[<ffffffff810bf879>] ? __do_fault+0x3a9/0x3e1
[<ffffffffa011b12f>] kvm_vm_ioctl+0x364/0x38d [kvm]
[<ffffffff81060cfa>] ? up_read+0x23/0x3d
[<ffffffff810f3587>] vfs_ioctl+0x32/0xa6
[<ffffffff810f3b19>] do_vfs_ioctl+0x495/0x4db
[<ffffffff810e6b2f>] ? fget_light+0xc2/0x241
[<ffffffff810e416c>] ? do_sys_open+0x104/0x116
[<ffffffff81382d6d>] ? retint_swapgs+0xe/0x13
[<ffffffff810f3ba6>] sys_ioctl+0x47/0x6a
[<ffffffff810021db>] system_call_fastpath+0x16/0x1b

Signed-off-by: Lai Jiangshan <laijs(a)cn.fujitsu.com>
---
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 73c5c2b..52b8ece 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1379,7 +1379,7 @@ static void kvm_release_vm_pages(struct kvm *kvm)
int i, j;
unsigned long base_gfn;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);
for (i = 0; i < slots->nmemslots; i++) {
memslot = &slots->memslots[i];
base_gfn = memslot->base_gfn;
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 60f09ab..cfa9d17 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -72,7 +72,7 @@ static inline void kvm_s390_vcpu_set_mem(struct kvm_vcpu *vcpu)
struct kvm_memslots *memslots;

idx = srcu_read_lock(&vcpu->kvm->srcu);
- memslots = rcu_dereference(vcpu->kvm->memslots);
+ memslots = kvm_memslots(vcpu->kvm);

mem = &memslots->memslots[0];

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 71faa04..bb61881 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -792,7 +792,7 @@ static int kvm_handle_hva(struct kvm *kvm, unsigned long hva,
int retval = 0;
struct kvm_memslots *slots;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);

for (i = 0; i < slots->nmemslots; i++) {
struct kvm_memory_slot *memslot = &slots->memslots[i];
@@ -3017,7 +3017,8 @@ unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
unsigned int nr_pages = 0;
struct kvm_memslots *slots;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);
+
for (i = 0; i < slots->nmemslots; i++)
nr_pages += slots->memslots[i].npages;

@@ -3292,7 +3293,7 @@ static int count_rmaps(struct kvm_vcpu *vcpu)
int i, j, k, idx;

idx = srcu_read_lock(&kvm->srcu);
- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);
for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
struct kvm_memory_slot *m = &slots->memslots[i];
struct kvm_rmap_desc *d;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 077cac5..725e7b6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1514,7 +1514,7 @@ static gva_t rmode_tss_base(struct kvm *kvm)
struct kvm_memslots *slots;
gfn_t base_gfn;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);
base_gfn = kvm->memslots->memslots[0].base_gfn +
kvm->memslots->memslots[0].npages - 3;
return base_gfn << PAGE_SHIFT;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6120e33..4dcd62c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2408,7 +2408,7 @@ gfn_t unalias_gfn_instantiation(struct kvm *kvm, gfn_t gfn)
struct kvm_mem_alias *alias;
struct kvm_mem_aliases *aliases;

- aliases = rcu_dereference(kvm->arch.aliases);
+ aliases = kvm_aliases(kvm);

for (i = 0; i < aliases->naliases; ++i) {
alias = &aliases->aliases[i];
@@ -2427,7 +2427,7 @@ gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
struct kvm_mem_alias *alias;
struct kvm_mem_aliases *aliases;

- aliases = rcu_dereference(kvm->arch.aliases);
+ aliases = kvm_aliases(kvm);

for (i = 0; i < aliases->naliases; ++i) {
alias = &aliases->aliases[i];
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 2d10163..e218fed 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -65,4 +65,11 @@ static inline int is_paging(struct kvm_vcpu *vcpu)
return kvm_read_cr0_bits(vcpu, X86_CR0_PG);
}

+static inline struct kvm_mem_aliases *kvm_aliases(struct kvm *kvm)
+{
+ return rcu_dereference_check(kvm->arch.aliases,
+ srcu_read_lock_held(&kvm->srcu)
+ || lockdep_is_held(&kvm->slots_lock));
+}
+
#endif
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a3fd0f9..f735752 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -239,6 +239,13 @@ void kvm_exit(void);
void kvm_get_kvm(struct kvm *kvm);
void kvm_put_kvm(struct kvm *kvm);

+static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
+{
+ return rcu_dereference_check(kvm->memslots,
+ srcu_read_lock_held(&kvm->srcu)
+ || lockdep_is_held(&kvm->slots_lock));
+}
+
#define HPA_MSB ((sizeof(hpa_t) * 8) - 1)
#define HPA_ERR_MASK ((hpa_t)1 << HPA_MSB)
static inline int is_error_hpa(hpa_t hpa) { return hpa >> HPA_MSB; }
diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index 80fd3ad..37ca71e 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -78,7 +78,7 @@ static int kvm_iommu_map_memslots(struct kvm *kvm)
int i, r = 0;
struct kvm_memslots *slots;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);

for (i = 0; i < slots->nmemslots; i++) {
r = kvm_iommu_map_pages(kvm, &slots->memslots[i]);
@@ -217,7 +217,7 @@ static int kvm_iommu_unmap_memslots(struct kvm *kvm)
int i;
struct kvm_memslots *slots;

- slots = rcu_dereference(kvm->memslots);
+ slots = kvm_memslots(kvm);

for (i = 0; i < slots->nmemslots; i++) {
kvm_iommu_put_pages(kvm, slots->memslots[i].base_gfn,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b03f863..58b2147 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -829,7 +829,7 @@ EXPORT_SYMBOL_GPL(kvm_is_error_hva);
struct kvm_memory_slot *gfn_to_memslot_unaliased(struct kvm *kvm, gfn_t gfn)
{
int i;
- struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
+ struct kvm_memslots *slots = kvm_memslots(kvm);

for (i = 0; i < slots->nmemslots; ++i) {
struct kvm_memory_slot *memslot = &slots->memslots[i];
@@ -851,7 +851,7 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
{
int i;
- struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
+ struct kvm_memslots *slots = kvm_memslots(kvm);

gfn = unalias_gfn_instantiation(kvm, gfn);
for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
@@ -895,7 +895,7 @@ out:
int memslot_id(struct kvm *kvm, gfn_t gfn)
{
int i;
- struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
+ struct kvm_memslots *slots = kvm_memslots(kvm);
struct kvm_memory_slot *memslot = NULL;

gfn = unalias_gfn(kvm, gfn);
@@ -1979,7 +1979,9 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, const void *val)
{
int i;
- struct kvm_io_bus *bus = rcu_dereference(kvm->buses[bus_idx]);
+ struct kvm_io_bus *bus;
+
+ bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
for (i = 0; i < bus->dev_count; i++)
if (!kvm_iodevice_write(bus->devs[i], addr, len, val))
return 0;
@@ -1991,8 +1993,9 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, void *val)
{
int i;
- struct kvm_io_bus *bus = rcu_dereference(kvm->buses[bus_idx]);
+ struct kvm_io_bus *bus;

+ bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
for (i = 0; i < bus->dev_count; i++)
if (!kvm_iodevice_read(bus->devs[i], addr, len, val))
return 0;

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Next: [BUG] kvm: dereference srcu-protected pointer without srcu_read_lock() held