Hi Gleb,
Please see below.
On 07/12/2014 03:44 PM, Gleb Natapov wrote:
On Wed, Jul 09, 2014 at 10:08:03AM +0800, Tang Chen wrote:
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.
Signed-off-by: Tang Chen<tangchen@xxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/vmx.c | 25 +++++++++++--------------
2 files changed, 11 insertions(+), 15 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4931415..62f973e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -578,7 +578,6 @@ 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 0918635e..fe2e5f4 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -741,6 +741,7 @@ 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 bool vmx_mpx_supported(void);
+static int alloc_identity_pagetable(struct kvm *kvm);
static DEFINE_PER_CPU(struct vmcs *, vmxarea);
static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
@@ -3921,21 +3922,21 @@ 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;
- }
if (likely(kvm->arch.ept_identity_pagetable_done))
return 1;
- ret = 0;
identity_map_pfn = kvm->arch.ept_identity_map_addr>> PAGE_SHIFT;
+
+ mutex_lock(&kvm->slots_lock);
Why move this out of alloc_identity_pagetable()?
Referring to the original code, I think mutex_lock(&kvm->slots_lock) is
used
to protect kvm->arch.ept_identity_pagetable. If two or more threads try to
modify it at the same time, the mutex ensures that the identity table is
only
allocated once.
Now, we dropped kvm->arch.ept_identity_pagetable. And use
kvm->arch.ept_identity_pagetable_done
to check if the identity table is allocated and initialized. So we
should protect
memory slot operation in alloc_identity_pagetable() and
kvm->arch.ept_identity_pagetable_done
with this mutex.
Of course, I can see that the name "slots_lock" indicates that it may be
used
to protect the memory slot operation only. Maybe move it out here is not
suitable.
If I'm wrong, please tell me.
+ 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)
@@ -3953,6 +3954,9 @@ 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;
}
@@ -4006,9 +4010,6 @@ static int alloc_identity_pagetable(struct kvm *kvm)
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 =
@@ -4025,9 +4026,7 @@ static int alloc_identity_pagetable(struct kvm *kvm)
goto out;
}
- kvm->arch.ept_identity_pagetable = page;
I think we can drop gfn_to_page() above too now. Why would we need it?
Yes, will remove it in the next version.
Thanks.
out:
- mutex_unlock(&kvm->slots_lock);
return r;
}
@@ -7583,8 +7582,6 @@ 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;
}
--
1.8.3.1
--
Gleb.
.
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