Re: [PATCH kernel 4/9] KVM: PPC: Use RCU for arch.spapr_tce_tables

[David Gibson]

On Tue, Sep 15, 2015 at 08:49:34PM +1000, Alexey Kardashevskiy wrote:
> At the moment spapr_tce_tables is not protected against races. This makes
> use of RCU-variants of list helpers. As some bits are executed in real
> mode, this makes use of just introduced list_for_each_entry_rcu_notrace().
> 
> This converts release_spapr_tce_table() to a RCU scheduled handler.
> 
> Signed-off-by: Alexey Kardashevskiy 

Looks correct on my limited knowledge of RCU

Reviewed-by: David Gibson 

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[PATCH kernel 4/9] KVM: PPC: Use RCU for arch.spapr_tce_tables

[Alexey Kardashevskiy]

At the moment spapr_tce_tables is not protected against races. This makes
use of RCU-variants of list helpers. As some bits are executed in real
mode, this makes use of just introduced list_for_each_entry_rcu_notrace().

This converts release_spapr_tce_table() to a RCU scheduled handler.

Signed-off-by: Alexey Kardashevskiy 
---
 arch/powerpc/include/asm/kvm_host.h |  1 +
 arch/powerpc/kvm/book3s.c   |  2 +-
 arch/powerpc/kvm/book3s_64_vio.c| 20 +++-
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h 
b/arch/powerpc/include/asm/kvm_host.h
index 98eebbf6..e19d412 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -178,6 +178,7 @@ struct kvmppc_spapr_tce_table {
struct kvm *kvm;
u64 liobn;
u32 window_size;
+   struct rcu_head rcu;
struct page *pages[0];
 };
 
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 53285d5..3418f7c 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -806,7 +806,7 @@ int kvmppc_core_init_vm(struct kvm *kvm)
 {
 
 #ifdef CONFIG_PPC64
-   INIT_LIST_HEAD(>arch.spapr_tce_tables);
+   INIT_LIST_HEAD_RCU(>arch.spapr_tce_tables);
INIT_LIST_HEAD(>arch.rtas_tokens);
 #endif
 
diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index 54cf9bc..9526c34 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -45,19 +45,16 @@ static long kvmppc_stt_npages(unsigned long window_size)
 * sizeof(u64), PAGE_SIZE) / PAGE_SIZE;
 }
 
-static void release_spapr_tce_table(struct kvmppc_spapr_tce_table *stt)
+static void release_spapr_tce_table(struct rcu_head *head)
 {
-   struct kvm *kvm = stt->kvm;
+   struct kvmppc_spapr_tce_table *stt = container_of(head,
+   struct kvmppc_spapr_tce_table, rcu);
int i;
 
-   mutex_lock(>lock);
-   list_del(>list);
for (i = 0; i < kvmppc_stt_npages(stt->window_size); i++)
__free_page(stt->pages[i]);
+
kfree(stt);
-   mutex_unlock(>lock);
-
-   kvm_put_kvm(kvm);
 }
 
 static int kvm_spapr_tce_fault(struct vm_area_struct *vma, struct vm_fault 
*vmf)
@@ -88,7 +85,12 @@ static int kvm_spapr_tce_release(struct inode *inode, struct 
file *filp)
 {
struct kvmppc_spapr_tce_table *stt = filp->private_data;
 
-   release_spapr_tce_table(stt);
+   list_del_rcu(>list);
+
+   kvm_put_kvm(stt->kvm);
+
+   call_rcu(>rcu, release_spapr_tce_table);
+
return 0;
 }
 
@@ -131,7 +133,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
kvm_get_kvm(kvm);
 
mutex_lock(>lock);
-   list_add(>list, >arch.spapr_tce_tables);
+   list_add_rcu(>list, >arch.spapr_tce_tables);
 
mutex_unlock(>lock);
 
-- 
2.4.0.rc3.8.gfb3e7d5

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