[PATCH 0/3] KVM: remove dummy pages

[PATCH 0/3] KVM: remove dummy pages

[Xiao Guangrong]

Currently, kvm allocates some pages and use then as error indicators,
it wastes memory and is not good for scalability.

In this patchset, we introduce some error code instead of the pages to
indicate the error conditions.

[PATCH 1/3] KVM: MMU: using kvm_release_pfn_clean to release pfn

[Xiao Guangrong]

The current code depends on fault_page is the normal page, but we will
use the error code instead of dummy page in the later patch, so using
kvm_release_pfn_clean to release pfn which will release error code probably

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
 arch/x86/kvm/mmu.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2419934..a9a2052 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3275,7 +3275,7 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 	if (!async)
 		return false; /* *pfn has correct page already */

-	put_page(pfn_to_page(*pfn));
+	kvm_release_pfn_clean(*pfn);

 	if (!prefault && can_do_async_pf(vcpu)) {
 		trace_kvm_try_async_get_page(gva, gfn);
-- 
1.7.7.6

[PATCH 2/3] KVM: use kvm_release_page_clean to guest page

[Xiao Guangrong]

In kvm_async_pf_wakeup_all, it uses bad_page to generate broadcast wakeup,
and use put_page to release the page, the work depends on bad_page is the
normal page. But we will use the error code instead of bad_page, so use
kvm_release_page_clean to release the page which will release the error
code probably

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
 virt/kvm/async_pf.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 74268b4..ebae24b 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -112,7 +112,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
 				   typeof(*work), link);
 		list_del(&work->link);
 		if (work->page)
-			put_page(work->page);
+			kvm_release_page_clean(work->page);
 		kmem_cache_free(async_pf_cache, work);
 	}
 	spin_unlock(&vcpu->async_pf.lock);
@@ -139,7 +139,7 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 		list_del(&work->queue);
 		vcpu->async_pf.queued--;
 		if (work->page)
-			put_page(work->page);
+			kvm_release_page_clean(work->page);
 		kmem_cache_free(async_pf_cache, work);
 	}
 }
-- 
1.7.7.6

[PATCH 3/3] KVM: remove dummy pages

[Xiao Guangrong]

Currently, kvm allocate some pages and use them as error indicators,
it wastes memory and is not good for scalability. So we use the error
code instead of the pages to indicate the error

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
 include/linux/kvm_host.h |    3 +-
 virt/kvm/async_pf.c      |    3 +-
 virt/kvm/kvm_main.c      |  121 +++++++++++++++++++---------------------------
 3 files changed, 52 insertions(+), 75 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6d1a51e..f4e132c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -411,6 +411,7 @@ void kvm_arch_flush_shadow(struct kvm *kvm);
 int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,
 			    int nr_pages);

+struct page *get_bad_page(void);
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
 unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn);
 void kvm_release_page_clean(struct page *page);
@@ -564,7 +565,7 @@ void kvm_arch_sync_events(struct kvm *kvm);
 int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
 void kvm_vcpu_kick(struct kvm_vcpu *vcpu);

-int kvm_is_mmio_pfn(pfn_t pfn);
+bool kvm_is_mmio_pfn(pfn_t pfn);

 struct kvm_irq_ack_notifier {
 	struct hlist_node link;
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index ebae24b..7972278 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -203,8 +203,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
 	if (!work)
 		return -ENOMEM;

-	work->page = bad_page;
-	get_page(bad_page);
+	work->page = get_bad_page();
 	INIT_LIST_HEAD(&work->queue); /* for list_del to work */

 	spin_lock(&vcpu->async_pf.lock);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index eb15833..92aae8b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -100,17 +100,11 @@ EXPORT_SYMBOL_GPL(kvm_rebooting);

 static bool largepages_enabled = true;

-struct page *bad_page;
-static pfn_t bad_pfn;
-
-static struct page *hwpoison_page;
-static pfn_t hwpoison_pfn;
-
-static struct page *fault_page;
-static pfn_t fault_pfn;
-
-inline int kvm_is_mmio_pfn(pfn_t pfn)
+bool kvm_is_mmio_pfn(pfn_t pfn)
 {
+	if (is_error_pfn(pfn))
+		return false;
+
 	if (pfn_valid(pfn)) {
 		int reserved;
 		struct page *tail = pfn_to_page(pfn);
@@ -936,34 +930,55 @@ EXPORT_SYMBOL_GPL(kvm_disable_largepages);

 int is_error_page(struct page *page)
 {
-	return page == bad_page || page == hwpoison_page || page == fault_page;
+	return IS_ERR(page);
 }
 EXPORT_SYMBOL_GPL(is_error_page);

 int is_error_pfn(pfn_t pfn)
 {
-	return pfn == bad_pfn || pfn == hwpoison_pfn || pfn == fault_pfn;
+	return IS_ERR_VALUE(pfn);
 }
 EXPORT_SYMBOL_GPL(is_error_pfn);

+static pfn_t get_bad_pfn(void)
+{
+	return -ENOENT;
+}
+
+pfn_t get_fault_pfn(void)
+{
+	return -EFAULT;
+}
+EXPORT_SYMBOL_GPL(get_fault_pfn);
+
+static pfn_t get_hwpoison_pfn(void)
+{
+	return -EHWPOISON;
+}
+
 int is_hwpoison_pfn(pfn_t pfn)
 {
-	return pfn == hwpoison_pfn;
+	return pfn == -EHWPOISON;
 }
 EXPORT_SYMBOL_GPL(is_hwpoison_pfn);

 int is_noslot_pfn(pfn_t pfn)
 {
-	return pfn == bad_pfn;
+	return pfn == -ENOENT;
 }
 EXPORT_SYMBOL_GPL(is_noslot_pfn);

 int is_invalid_pfn(pfn_t pfn)
 {
-	return pfn == hwpoison_pfn || pfn == fault_pfn;
+	return !is_noslot_pfn(pfn) && is_error_pfn(pfn);
 }
 EXPORT_SYMBOL_GPL(is_invalid_pfn);

+struct page *get_bad_page(void)
+{
+	return ERR_PTR(-ENOENT);
+}
+
 static inline unsigned long bad_hva(void)
 {
 	return PAGE_OFFSET;
@@ -1035,13 +1050,6 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(gfn_to_hva);

-pfn_t get_fault_pfn(void)
-{
-	get_page(fault_page);
-	return fault_pfn;
-}
-EXPORT_SYMBOL_GPL(get_fault_pfn);
-
 int get_user_page_nowait(struct task_struct *tsk, struct mm_struct *mm,
 	unsigned long start, int write, struct page **page)
 {
@@ -1119,8 +1127,7 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 		if (npages == -EHWPOISON ||
 			(!async && check_user_page_hwpoison(addr))) {
 			up_read(&current->mm->mmap_sem);
-			get_page(hwpoison_page);
-			return page_to_pfn(hwpoison_page);
+			return get_hwpoison_pfn();
 		}

 		vma = find_vma_intersection(current->mm, addr, addr+1);
@@ -1158,10 +1165,8 @@ static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async,
 		*async = false;

 	addr = gfn_to_hva(kvm, gfn);
-	if (kvm_is_error_hva(addr)) {
-		get_page(bad_page);
-		return page_to_pfn(bad_page);
-	}
+	if (kvm_is_error_hva(addr))
+		return get_bad_pfn();

 	return hva_to_pfn(addr, atomic, async, write_fault, writable);
 }
@@ -1215,37 +1220,45 @@ int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,
 }
 EXPORT_SYMBOL_GPL(gfn_to_page_many_atomic);

+static struct page *kvm_pfn_to_page(pfn_t pfn)
+{
+	WARN_ON(kvm_is_mmio_pfn(pfn));
+
+	if (is_error_pfn(pfn) || kvm_is_mmio_pfn(pfn))
+		return get_bad_page();
+
+	return pfn_to_page(pfn);
+}
+
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 {
 	pfn_t pfn;

 	pfn = gfn_to_pfn(kvm, gfn);
-	if (!kvm_is_mmio_pfn(pfn))
-		return pfn_to_page(pfn);
-
-	WARN_ON(kvm_is_mmio_pfn(pfn));

-	get_page(bad_page);
-	return bad_page;
+	return kvm_pfn_to_page(pfn);
 }

 EXPORT_SYMBOL_GPL(gfn_to_page);

 void kvm_release_page_clean(struct page *page)
 {
-	kvm_release_pfn_clean(page_to_pfn(page));
+	if (!is_error_page(page))
+		kvm_release_pfn_clean(page_to_pfn(page));
 }
 EXPORT_SYMBOL_GPL(kvm_release_page_clean);

 void kvm_release_pfn_clean(pfn_t pfn)
 {
-	if (!kvm_is_mmio_pfn(pfn))
+	if (!is_error_pfn(pfn) && !kvm_is_mmio_pfn(pfn))
 		put_page(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);

 void kvm_release_page_dirty(struct page *page)
 {
+	WARN_ON(is_error_page(page));
+
 	kvm_release_pfn_dirty(page_to_pfn(page));
 }
 EXPORT_SYMBOL_GPL(kvm_release_page_dirty);
@@ -2724,33 +2737,6 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 	if (r)
 		goto out_fail;

-	bad_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-
-	if (bad_page == NULL) {
-		r = -ENOMEM;
-		goto out;
-	}
-
-	bad_pfn = page_to_pfn(bad_page);
-
-	hwpoison_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-
-	if (hwpoison_page == NULL) {
-		r = -ENOMEM;
-		goto out_free_0;
-	}
-
-	hwpoison_pfn = page_to_pfn(hwpoison_page);
-
-	fault_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-
-	if (fault_page == NULL) {
-		r = -ENOMEM;
-		goto out_free_0;
-	}
-
-	fault_pfn = page_to_pfn(fault_page);
-
 	if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) {
 		r = -ENOMEM;
 		goto out_free_0;
@@ -2825,12 +2811,6 @@ out_free_1:
 out_free_0a:
 	free_cpumask_var(cpus_hardware_enabled);
 out_free_0:
-	if (fault_page)
-		__free_page(fault_page);
-	if (hwpoison_page)
-		__free_page(hwpoison_page);
-	__free_page(bad_page);
-out:
 	kvm_arch_exit();
 out_fail:
 	return r;
@@ -2850,8 +2830,5 @@ void kvm_exit(void)
 	kvm_arch_hardware_unsetup();
 	kvm_arch_exit();
 	free_cpumask_var(cpus_hardware_enabled);
-	__free_page(fault_page);
-	__free_page(hwpoison_page);
-	__free_page(bad_page);
 }
 EXPORT_SYMBOL_GPL(kvm_exit);
-- 
1.7.7.6

Re: [PATCH 0/3] KVM: remove dummy pages

[Xiao Guangrong]

On 07/23/2012 10:03 PM, Xiao Guangrong wrote:
> Currently, kvm allocates some pages and use then as error indicators,
> it wastes memory and is not good for scalability.
> 
> In this patchset, we introduce some error code instead of the pages to
> indicate the error conditions.
> 

Sorry for the noise, there are some typos in the title and in the change-logs,
I will correct them after you guys review the patches.