Re: [PATCH v7 000/102] KVM TDX basic feature support

Chao Peng
2022-07-20T15:04:27Z

On Thu, Jul 14, 2022 at 01:03:46AM +0000, Sean Christopherson wrote:
...
>
> Option D). track shared regions in an Xarray, update kvm_arch_memory_slot.lpage_info
> on insertion/removal to (dis)allow hugepages as needed.
>
> + efficient on KVM page fault (no new lookups)
> + zero memory overhead (assuming KVM has to eat the cost of the Xarray anyways)
> + straightforward to implement
> + can (and should) be merged as part of the UPM series
>
> I believe xa_for_each_range() can be used to see if a given 2mb/1gb range is
> completely covered (fully shared) or not covered at all (fully private), but I'm
> not 100% certain that xa_for_each_range() works the way I think it does.

Hi Sean,

Below is the implementation to support 2M as you mentioned as option D.
It's based on UPM v7 xarray code: https://lkml.org/lkml/2022/7/6/259

Everything sounds good, the only trick bit is inc/dec disallow_lpage. If
we still treat it as a count, it will be a challenge to make the inc/dec
balanced. So in this patch I stole a bit for the purpose, looks ugly.

Any feedback is welcome.

Thanks,
Chao

-----------------------------------------------------------------------
From: Chao Peng <chao.p.peng@linux.intel.com>
Date: Wed, 20 Jul 2022 11:37:18 +0800
Subject: [PATCH] KVM: Add large page support for private memory

Update lpage_info when handling KVM_MEMORY_ENCRYPT_{UN,}REG_REGION.

Reserve a bit in disallow_lpage to indicate a large page has
private/share pages mixed.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
arch/x86/include/asm/kvm_host.h | 8 +++
arch/x86/kvm/mmu/mmu.c | 120 +++++++++++++++++++++++++++++++-
include/linux/kvm_host.h | 14 ++++
virt/kvm/kvm_main.c | 12 +++-
4 files changed, 150 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d460b8511041..b6ffe8b1c547 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

@@ -935,6 +936,13 @@ 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 771ffd147e77..d040eeaf1f1c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -843,11 +843,16 @@ 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);
}
}

@@ -7246,3 +7251,116 @@ 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 & 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);
+ }
+
+ 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);
+ }
+ }
+}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d45f00f5b3ee..7b18fcd71df5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2282,6 +2282,10 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
#define KVM_DIRTY_RING_MAX_ENTRIES 65536

#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
+
+#define KVM_MEM_ATTR_SHARED 0x0001
+#define KVM_MEM_ATTR_PRIVATE 0x0002
+
static inline int kvm_private_mem_get_pfn(struct kvm_memory_slot *slot,
gfn_t gfn, kvm_pfn_t *pfn, int *order)
{
@@ -2307,6 +2311,16 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
return !!xa_load(&kvm->mem_attr_array, gfn);
}

+#ifdef __KVM_HAVE_ARCH_UPDATE_MEM_ATTR
+void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
+ gfn_t start, gfn_t end);
+#else
+static inline void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
+ gfn_t start, gfn_t end)
+{
+}
+#endif
+
#endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */

#endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1ba4b9e5449c..1d22c8603f91 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -863,12 +863,12 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
#endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
-#define KVM_MEM_ATTR_PRIVATE 0x0001
static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl,
struct kvm_enc_region *region)
{
unsigned long start, end;
void *entry;
+ int attr;
int r;

if (region->size == 0 || region->addr + region->size < region->addr)
@@ -879,13 +879,19 @@ static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl
start = region->addr >> PAGE_SHIFT;
end = (region->addr + region->size - 1) >> PAGE_SHIFT;

- entry = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION ?
- xa_mk_value(KVM_MEM_ATTR_PRIVATE) : NULL;
+ if (ioctl == KVM_MEMORY_ENCRYPT_REG_REGION) {
+ attr = KVM_MEM_ATTR_PRIVATE;
+ entry = xa_mk_value(KVM_MEM_ATTR_PRIVATE);
+ } else {
+ attr = KVM_MEM_ATTR_SHARED;
+ entry = NULL;
+ }

r = xa_err(xa_store_range(&kvm->mem_attr_array, start, end,
entry, GFP_KERNEL_ACCOUNT));

kvm_zap_gfn_range(kvm, start, end + 1);
+ kvm_arch_update_mem_attr(kvm, attr, start, end + 1);

return r;
}
--
2