Re: [PATCH v8 6/8] KVM: Update lpage info when private/shared memory are mixed
On Thu, Sep 29, 2022 at 09:52:06AM -0700, Isaku Yamahata wrote:
> On Thu, Sep 15, 2022 at 10:29:11PM +0800,
> Chao Peng wrote:
>
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 08abad4f3e6f..a0f198cede3d 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> ...
> > @@ -6894,3 +6899,115 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> > if (kvm->arch.nx_lpage_recovery_thread)
> > kthread_stop(kvm->arch.nx_lpage_recovery_thread);
> > }
> > +
> > +static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + XA_STATE(xas, &kvm->mem_attr_array, start);
> > + gfn_t gfn = start;
> > + void *entry;
> > + bool shared, private;
> > + bool mixed = false;
> > +
> > + if (attr == KVM_MEM_ATTR_SHARED) {
> > + shared = true;
> > + private = false;
> > + } else {
> > + shared = false;
> > + private = true;
> > + }
>
> We don't have to care the target is shared or private. We need to check
> only same or not.
There is optimization chance if we know what we are going to set. we can
return 'mixed = true' earlier when we find the first reverse attr, e.g.
it's unnecessarily to check all the child page attr in one largepage to
give a conclusion.
After a further look, the code can be refined as below:
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7255,17 +7255,9 @@ static bool mem_attr_is_mixed(struct kvm *kvm, unsigned
int attr,
XA_STATE(xas, &kvm->mem_attr_array, start);
gfn_t gfn = start;
void *entry;
- bool shared, private;
+ bool shared = attr == KVM_MEM_ATTR_SHARED;
bool mixed = false;
- if (attr == KVM_MEM_ATTR_SHARED) {
- shared = true;
- private = false;
- } else {
- shared = false;
- private = true;
- }
-
rcu_read_lock();
entry = xas_load(&xas);
while (gfn < end) {
@@ -7274,12 +7266,7 @@ static bool mem_attr_is_mixed(struct kvm *kvm, unsigned
int attr,
KVM_BUG_ON(gfn != xas.xa_index, kvm);
- if (entry)
- private = true;
- else
- shared = true;
-
- if (private && shared) {
+ if ((entry && !shared) || (!entry && shared)) {
mixed = true;
goto out;
}
@@ -7320,8 +7307,7 @@ static void update_mem_lpage_info(struct kvm *kvm,
* we know they are not mixed.
*/
update_mixed(lpage_info_slot(lpage_start, slot, level),
-mem_attr_is_mixed(kvm, attr, lpage_start,
- lpage_start + pages));
+mem_attr_is_mixed(kvm, attr, lpage_start, start));
if (lpage_start == lpage_end)
return;
@@ -7330,7 +7316,7 @@ static void update_mem_lpage_info(struct kvm *kvm,
update_mixed(lpage_info_slot(gfn, slot, level), false);
update_mixed(lpage_info_slot(lpage_end, slot, level),
-mem_attr_is_mixed(kvm, attr, lpage_end,
+mem_attr_is_mixed(kvm, attr, end,
lpage_end + pages));
}
}
>
> > +
> > + rcu_read_lock();
> > + entry = xas_load(&xas);
> > + while (gfn < end) {
> > + if (xas_retry(&xas, entry))
> > + continue;
> > +
> > + KVM_BUG_ON(gfn != xas.xa_index, kvm);
> > +
> > + if (entry)
> > + private = true;
> > + else
> > + shared = true;
> > +
> > + if (private && shared) {
> > + mixed = true;
> > + goto out;
> > + }
> > +
> > + entry = xas_next(&xas);
> > + gfn++;
> > + }
> > +out:
> > + rcu_read_unlock();
> > + return mixed;
> > +}
> > +
> > +static inline void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
> > +{
> > + if (mixed)
> > + linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > + else
> > + linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +}
> > +
> > +static void update_mem_lpage_info(struct kvm *kvm,
> > + struct kvm_memory_slot *slot,
> > + unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + unsigned long lpage_start, lpage_end;
> > + unsigned long gfn, pages, mask;
> > + int level;
> > +
> > + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > + pages = KVM_PAGES_PER_HPAGE(level);
> > + mask = ~(pages - 1);
> > + lpage_start = start & mask;
> > + lpag
Re: [PATCH v8 6/8] KVM: Update lpage info when private/shared memory are mixed
On Thu, Sep 15, 2022 at 10:29:11PM +0800,
Chao Peng wrote:
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 08abad4f3e6f..a0f198cede3d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
...
> @@ -6894,3 +6899,115 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> if (kvm->arch.nx_lpage_recovery_thread)
> kthread_stop(kvm->arch.nx_lpage_recovery_thread);
> }
> +
> +static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
> + gfn_t start, gfn_t end)
> +{
> + XA_STATE(xas, &kvm->mem_attr_array, start);
> + gfn_t gfn = start;
> + void *entry;
> + bool shared, private;
> + bool mixed = false;
> +
> + if (attr == KVM_MEM_ATTR_SHARED) {
> + shared = true;
> + private = false;
> + } else {
> + shared = false;
> + private = true;
> + }
We don't have to care the target is shared or private. We need to check
only same or not.
> +
> + rcu_read_lock();
> + entry = xas_load(&xas);
> + while (gfn < end) {
> + if (xas_retry(&xas, entry))
> + continue;
> +
> + KVM_BUG_ON(gfn != xas.xa_index, kvm);
> +
> + if (entry)
> + private = true;
> + else
> + shared = true;
> +
> + if (private && shared) {
> + mixed = true;
> + goto out;
> + }
> +
> + entry = xas_next(&xas);
> + gfn++;
> + }
> +out:
> + rcu_read_unlock();
> + return mixed;
> +}
> +
> +static inline void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
> +{
> + if (mixed)
> + linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> + else
> + linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> +}
> +
> +static void update_mem_lpage_info(struct kvm *kvm,
> + struct kvm_memory_slot *slot,
> + unsigned int attr,
> + gfn_t start, gfn_t end)
> +{
> + unsigned long lpage_start, lpage_end;
> + unsigned long gfn, pages, mask;
> + int level;
> +
> + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> + pages = KVM_PAGES_PER_HPAGE(level);
> + mask = ~(pages - 1);
> + lpage_start = start & mask;
> + lpage_end = (end - 1) & mask;
> +
> + /*
> + * We only need to scan the head and tail page, for middle pages
> + * we know they are not mixed.
> + */
> + update_mixed(lpage_info_slot(lpage_start, slot, level),
> + mem_attr_is_mixed(kvm, attr, lpage_start,
> + lpage_start + pages));
> +
> + if (lpage_start == lpage_end)
> + return;
> +
> + for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> + update_mixed(lpage_info_slot(gfn, slot, level), false);
For >2M case, we don't have to check all entry. just check lower level case.
> +
> + update_mixed(lpage_info_slot(lpage_end, slot, level),
> + mem_attr_is_mixed(kvm, attr, lpage_end,
> + lpage_end + pages));
> + }
> +}
> +
> +void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
> + gfn_t start, gfn_t end)
> +{
> + struct kvm_memory_slot *slot;
> + struct kvm_memslots *slots;
> + struct kvm_memslot_iter iter;
> + int i;
> +
> + WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> + "Unsupported mem attribute.\n");
> +
> + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> + slots = __kvm_memslots(kvm, i);
> +
> + kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> + slot = iter.slot;
> + start = max(start, slot->base_gfn);
> + end = min(end, slot->base_gfn + slot->npages);
> + if (WARN_ON_ONCE(start >= end))
> + continue;
> +
> + update_mem_lpage_info(kvm, slot, attr, start, end);
> + }
> + }
> +}
Here is my updated version.
bool kvm_mem_attr_is_mixed(struct kvm_memory_slot *slot, gfn_t gfn, int level)
{
gfn_t pages = KVM_PAGES_PER_HPAGE(level);
gfn_t mask = ~(pages - 1);
struct kvm_lpage_info *linfo = lpage_info_slot(gfn & mask, slot, level);
WARN_ON_ONCE(level == PG_LEVEL_4K);
return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
}
#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM_ATTR
static void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
{
if (mixed)
linfo->disallow_lpage |=
[PATCH v8 6/8] KVM: Update lpage info when private/shared memory are mixed
When private/shared memory are mixed in a large page, the lpage_info may
not be accurate and should be updated with this mixed info. A large page
has mixed pages can't be really mapped as large page since its
private/shared pages are from different physical memory.
This patch updates lpage_info when private/shared memory attribute is
changed. If both private and shared pages are within a large page
region, it can't be mapped as large page. It's a bit challenge to track
the mixed info in a 'count' like variable, this patch instead reserves a
bit in disallow_lpage to indicate a large page include mixed
private/share pages.
Signed-off-by: Chao Peng
---
arch/x86/include/asm/kvm_host.h | 8 +++
arch/x86/kvm/mmu/mmu.c | 119 +++-
arch/x86/kvm/x86.c | 2 +
include/linux/kvm_host.h| 17 +
virt/kvm/kvm_main.c | 11 ++-
5 files changed, 154 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cfad6ba1a70a..85119ed9527a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -38,6 +38,7 @@
#define __KVM_HAVE_ARCH_VCPU_DEBUGFS
#define __KVM_HAVE_ZAP_GFN_RANGE
+#define __KVM_HAVE_ARCH_UPDATE_MEM_ATTR
#define KVM_MAX_VCPUS 1024
@@ -945,6 +946,13 @@ struct kvm_vcpu_arch {
#endif
};
+/*
+ * Use a bit in disallow_lpage to indicate private/shared pages mixed at the
+ * level. The remaining bits will be used as a reference count for other users.
+ */
+#define KVM_LPAGE_PRIVATE_SHARED_MIXED (1U << 31)
+#define KVM_LPAGE_COUNT_MAX((1U << 31) - 1)
+
struct kvm_lpage_info {
int disallow_lpage;
};
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 08abad4f3e6f..a0f198cede3d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -762,11 +762,16 @@ static void update_gfn_disallow_lpage_count(const struct
kvm_memory_slot *slot,
{
struct kvm_lpage_info *linfo;
int i;
+ int disallow_count;
for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
linfo = lpage_info_slot(gfn, slot, i);
+
+ disallow_count = linfo->disallow_lpage & KVM_LPAGE_COUNT_MAX;
+ WARN_ON(disallow_count + count < 0 ||
+ disallow_count > KVM_LPAGE_COUNT_MAX - count);
+
linfo->disallow_lpage += count;
- WARN_ON(linfo->disallow_lpage < 0);
}
}
@@ -6894,3 +6899,115 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
if (kvm->arch.nx_lpage_recovery_thread)
kthread_stop(kvm->arch.nx_lpage_recovery_thread);
}
+
+static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
+ gfn_t start, gfn_t end)
+{
+ XA_STATE(xas, &kvm->mem_attr_array, start);
+ gfn_t gfn = start;
+ void *entry;
+ bool shared, private;
+ bool mixed = false;
+
+ if (attr == KVM_MEM_ATTR_SHARED) {
+ shared = true;
+ private = false;
+ } else {
+ shared = false;
+ private = true;
+ }
+
+ rcu_read_lock();
+ entry = xas_load(&xas);
+ while (gfn < end) {
+ if (xas_retry(&xas, entry))
+ continue;
+
+ KVM_BUG_ON(gfn != xas.xa_index, kvm);
+
+ if (entry)
+ private = true;
+ else
+ shared = true;
+
+ if (private && shared) {
+ mixed = true;
+ goto out;
+ }
+
+ entry = xas_next(&xas);
+ gfn++;
+ }
+out:
+ rcu_read_unlock();
+ return mixed;
+}
+
+static inline void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
+{
+ if (mixed)
+ linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
+ else
+ linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
+}
+
+static void update_mem_lpage_info(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ unsigned int attr,
+ gfn_t start, gfn_t end)
+{
+ unsigned long lpage_start, lpage_end;
+ unsigned long gfn, pages, mask;
+ int level;
+
+ for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
+ pages = KVM_PAGES_PER_HPAGE(level);
+ mask = ~(pages - 1);
+ lpage_start = start & mask;
+ lpage_end = (end - 1) & mask;
+
+ /*
+* We only need to scan the head and tail page, for middle pages
+* we know they are not mixed.
+*/
+ update_mixed(lpage_info_slot(lpage_start, slot, level),
+mem_attr_is_mixed(kvm, attr, lpage_start,
+
