[PATCH v5 2/7] kvm: Remove ept_identity_pagetable from struct kvm_arch.

Tang Chen
2014-09-11T05:36:56Z

kvm_arch->ept_identity_pagetable holds the ept identity pagetable page. But
it is never used to refer to the page at all.

In vcpu initialization, it indicates two things:
1. indicates if ept page is allocated
2. indicates if a memory slot for identity page is initialized

Actually, kvm_arch->ept_identity_pagetable_done is enough to tell if the ept
identity pagetable is initialized. So we can remove ept_identity_pagetable.

NOTE: In the original code, ept identity pagetable page is pinned in memroy.
As a result, it cannot be migrated/hot-removed. After this patch, since
kvm_arch->ept_identity_pagetable is removed, ept identity pagetable page
is no longer pinned in memory. And it can be migrated/hot-removed.

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Reviewed-by: Gleb Natapov <gleb@kernel.org>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/vmx.c | 50 ++++++++++++++++++++---------------------
arch/x86/kvm/x86.c | 2 --
3 files changed, 25 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7c492ed..35171c7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -580,7 +580,6 @@ struct kvm_arch {

gpa_t wall_clock;

- struct page *ept_identity_pagetable;
bool ept_identity_pagetable_done;
gpa_t ept_identity_map_addr;

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4b80ead..953d529 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -743,6 +743,7 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var);
static void vmx_sync_pir_to_irr_dummy(struct kvm_vcpu *vcpu);
static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx);
static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx);
+static int alloc_identity_pagetable(struct kvm *kvm);

static DEFINE_PER_CPU(struct vmcs *, vmxarea);
static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
@@ -3938,21 +3939,27 @@ out:

static int init_rmode_identity_map(struct kvm *kvm)
{
- int i, idx, r, ret;
+ int i, idx, r, ret = 0;
pfn_t identity_map_pfn;
u32 tmp;

if (!enable_ept)
return 1;
- if (unlikely(!kvm->arch.ept_identity_pagetable)) {
- printk(KERN_ERR "EPT: identity-mapping pagetable "
- "haven't been allocated!\n");
- return 0;
+
+ /* Protect kvm->arch.ept_identity_pagetable_done. */
+ mutex_lock(&kvm->slots_lock);
+
+ if (likely(kvm->arch.ept_identity_pagetable_done)) {
+ ret = 1;
+ goto out2;
}
- if (likely(kvm->arch.ept_identity_pagetable_done))
- return 1;
- ret = 0;
+
identity_map_pfn = kvm->arch.ept_identity_map_addr >> PAGE_SHIFT;
+
+ r = alloc_identity_pagetable(kvm);
+ if (r)
+ goto out2;
+
idx = srcu_read_lock(&kvm->srcu);
r = kvm_clear_guest_page(kvm, identity_map_pfn, 0, PAGE_SIZE);
if (r < 0)
@@ -3970,6 +3977,9 @@ static int init_rmode_identity_map(struct kvm *kvm)
ret = 1;
out:
srcu_read_unlock(&kvm->srcu, idx);
+
+out2:
+ mutex_unlock(&kvm->slots_lock);
return ret;
}

@@ -4019,31 +4029,23 @@ out:

static int alloc_identity_pagetable(struct kvm *kvm)
{
- struct page *page;
+ /*
+ * In init_rmode_identity_map(), kvm->arch.ept_identity_pagetable_done
+ * is checked before calling this function and set to true after the
+ * calling. The access to kvm->arch.ept_identity_pagetable_done should
+ * be protected by kvm->slots_lock.
+ */
+
struct kvm_userspace_memory_region kvm_userspace_mem;
int r = 0;

- mutex_lock(&kvm->slots_lock);
- if (kvm->arch.ept_identity_pagetable)
- goto out;
kvm_userspace_mem.slot = IDENTITY_PAGETABLE_PRIVATE_MEMSLOT;
kvm_userspace_mem.flags = 0;
kvm_userspace_mem.guest_phys_addr =
kvm->arch.ept_identity_map_addr;
kvm_userspace_mem.memory_size = PAGE_SIZE;
r = __kvm_set_memory_region(kvm, &kvm_userspace_mem);
- if (r)
- goto out;

- page = gfn_to_page(kvm, kvm->arch.ept_identity_map_addr >> PAGE_SHIFT);
- if (is_error_page(page)) {
- r = -EFAULT;
- goto out;
- }
-
- kvm->arch.ept_identity_pagetable = page;
-out:
- mutex_unlock(&kvm->slots_lock);
return r;
}

@@ -7643,8 +7645,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
kvm->arch.ept_identity_map_addr =
VMX_EPT_IDENTITY_PAGETABLE_ADDR;
err = -ENOMEM;
- if (alloc_identity_pagetable(kvm) != 0)
- goto free_vmcs;
if (!init_rmode_identity_map(kvm))
goto free_vmcs;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8f1e22d..e05bd58 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7239,8 +7239,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kvm_free_vcpus(kvm);
if (kvm->arch.apic_access_page)
put_page(kvm->arch.apic_access_page);
- if (kvm->arch.ept_identity_pagetable)
- put_page(kvm->arch.ept_identity_pagetable);
kfree(rcu_dereference_check(kvm->arch.apic_map, 1));
}

--
1.8.3.1