Re: [PATCH v2 6/6] KVM: MMU: init kvm generation close to mmio wrap-around value

2013-04-25 Thread Xiao Guangrong 
On 04/24/2013 08:59 PM, Gleb Natapov wrote:
 On Mon, Apr 01, 2013 at 05:56:49PM +0800, Xiao Guangrong wrote:
 Then it has chance to trigger mmio generation number wrap-around

 Signed-off-by: Xiao Guangrong xiaoguangr...@linux.vnet.ibm.com
 ---
  arch/x86/include/asm/kvm_host.h |1 +
  arch/x86/kvm/mmu.c  |8 
  virt/kvm/kvm_main.c |6 ++
  3 files changed, 15 insertions(+), 0 deletions(-)

 diff --git a/arch/x86/include/asm/kvm_host.h 
 b/arch/x86/include/asm/kvm_host.h
 index 6c1e642..4e1f7cb 100644
 --- a/arch/x86/include/asm/kvm_host.h
 +++ b/arch/x86/include/asm/kvm_host.h
 @@ -767,6 +767,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
   struct kvm_memory_slot *slot,
   gfn_t gfn_offset, unsigned long mask);
  void kvm_mmu_zap_all(struct kvm *kvm);
 +void kvm_arch_init_generation(struct kvm *kvm);
  void kvm_mmu_invalid_mmio_sptes(struct kvm *kvm);
  unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
  void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int 
 kvm_nr_mmu_pages);
 diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
 index d314e21..dcc059c 100644
 --- a/arch/x86/kvm/mmu.c
 +++ b/arch/x86/kvm/mmu.c
 @@ -4279,6 +4279,14 @@ restart:
  spin_unlock(kvm-mmu_lock);
  }
  
 +void kvm_arch_init_generation(struct kvm *kvm)
 +{
 +mutex_lock(kvm-slots_lock);
 +/* It is easier to trigger mmio generation-number wrap-around. */
 +kvm_memslots(kvm)-generation = MMIO_MAX_GEN - 13;
 kvm_memslots(kvm)-generation should never overflow since
 (read|write)_cached mechanism does not handle it. Initialising it to
 anything but 0 makes overflow more likely.
 
 You can hide mmio overflow trick in kvm_current_mmio_generation():
 
 static unsigned int kvm_current_mmio_generation(struct kvm *kvm)
 {
   return (kvm_memslots(kvm)-generation + MMIO_MAX_GEN - 13)  
 MMIO_GEN_MASK;
 }

Very smart idea. Thanks you, Gleb!



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Re: [PATCH v2 6/6] KVM: MMU: init kvm generation close to mmio wrap-around value

2013-04-24 Thread Gleb Natapov 
On Mon, Apr 01, 2013 at 05:56:49PM +0800, Xiao Guangrong wrote:
 Then it has chance to trigger mmio generation number wrap-around
 
 Signed-off-by: Xiao Guangrong xiaoguangr...@linux.vnet.ibm.com
 ---
  arch/x86/include/asm/kvm_host.h |1 +
  arch/x86/kvm/mmu.c  |8 
  virt/kvm/kvm_main.c |6 ++
  3 files changed, 15 insertions(+), 0 deletions(-)
 
 diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
 index 6c1e642..4e1f7cb 100644
 --- a/arch/x86/include/asm/kvm_host.h
 +++ b/arch/x86/include/asm/kvm_host.h
 @@ -767,6 +767,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn_offset, unsigned long mask);
  void kvm_mmu_zap_all(struct kvm *kvm);
 +void kvm_arch_init_generation(struct kvm *kvm);
  void kvm_mmu_invalid_mmio_sptes(struct kvm *kvm);
  unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
  void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int 
 kvm_nr_mmu_pages);
 diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
 index d314e21..dcc059c 100644
 --- a/arch/x86/kvm/mmu.c
 +++ b/arch/x86/kvm/mmu.c
 @@ -4279,6 +4279,14 @@ restart:
   spin_unlock(kvm-mmu_lock);
  }
  
 +void kvm_arch_init_generation(struct kvm *kvm)
 +{
 + mutex_lock(kvm-slots_lock);
 + /* It is easier to trigger mmio generation-number wrap-around. */
 + kvm_memslots(kvm)-generation = MMIO_MAX_GEN - 13;
kvm_memslots(kvm)-generation should never overflow since
(read|write)_cached mechanism does not handle it. Initialising it to
anything but 0 makes overflow more likely.

You can hide mmio overflow trick in kvm_current_mmio_generation():

static unsigned int kvm_current_mmio_generation(struct kvm *kvm)
{
return (kvm_memslots(kvm)-generation + MMIO_MAX_GEN - 13)  
MMIO_GEN_MASK;
}

--
Gleb.
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[PATCH v2 6/6] KVM: MMU: init kvm generation close to mmio wrap-around value

2013-04-01 Thread Xiao Guangrong 
Then it has chance to trigger mmio generation number wrap-around

Signed-off-by: Xiao Guangrong xiaoguangr...@linux.vnet.ibm.com
---
 arch/x86/include/asm/kvm_host.h |1 +
 arch/x86/kvm/mmu.c  |8 
 virt/kvm/kvm_main.c |6 ++
 3 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6c1e642..4e1f7cb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -767,6 +767,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
 struct kvm_memory_slot *slot,
 gfn_t gfn_offset, unsigned long mask);
 void kvm_mmu_zap_all(struct kvm *kvm);
+void kvm_arch_init_generation(struct kvm *kvm);
 void kvm_mmu_invalid_mmio_sptes(struct kvm *kvm);
 unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d314e21..dcc059c 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4279,6 +4279,14 @@ restart:
spin_unlock(kvm-mmu_lock);
 }
 
+void kvm_arch_init_generation(struct kvm *kvm)
+{
+   mutex_lock(kvm-slots_lock);
+   /* It is easier to trigger mmio generation-number wrap-around. */
+   kvm_memslots(kvm)-generation = MMIO_MAX_GEN - 13;
+   mutex_unlock(kvm-slots_lock);
+}
+
 void kvm_mmu_invalid_mmio_sptes(struct kvm *kvm)
 {
/*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ff71541..d21694a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -459,6 +459,10 @@ static void kvm_init_memslots_id(struct kvm *kvm)
slots-id_to_index[i] = slots-memslots[i].id = i;
 }
 
+void __attribute__((weak)) kvm_arch_init_generation(struct kvm *kvm)
+{
+}
+
 static struct kvm *kvm_create_vm(unsigned long type)
 {
int r, i;
@@ -505,6 +509,8 @@ static struct kvm *kvm_create_vm(unsigned long type)
mutex_init(kvm-slots_lock);
atomic_set(kvm-users_count, 1);
 
+   kvm_arch_init_generation(kvm);
+
r = kvm_init_mmu_notifier(kvm);
if (r)
goto out_err;
-- 
1.7.7.6

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