[RFC PATCH 3/6] KVM: SVM: Implement demand page pinning

Nikunj A Dadhania
2022-01-18T11:07:12Z

Use the memslot metadata to store the pinned data along with the pfns.
This improves the SEV guest startup time from O(n) to a constant by
deferring guest page pinning until the pages are used to satisfy nested
page faults. The page reference will be dropped in the memslot free
path.

Remove the enc_region structure definition and the code which did
upfront pinning, as they are no longer needed in view of the demand
pinning support.

Leave svm_register_enc_region() and svm_unregister_enc_region() as stubs
since qemu is dependent on this API.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
---
arch/x86/kvm/svm/sev.c | 208 ++++++++++++++++-------------------------
arch/x86/kvm/svm/svm.c | 1 +
arch/x86/kvm/svm/svm.h | 3 +-
3 files changed, 81 insertions(+), 131 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index d972ab4956d4..a962bed97a0b 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -66,14 +66,6 @@ static unsigned int nr_asids;
static unsigned long *sev_asid_bitmap;
static unsigned long *sev_reclaim_asid_bitmap;

-struct enc_region {
- struct list_head list;
- unsigned long npages;
- struct page **pages;
- unsigned long uaddr;
- unsigned long size;
-};
-
/* Called with the sev_bitmap_lock held, or on shutdown */
static int sev_flush_asids(int min_asid, int max_asid)
{
@@ -257,8 +249,6 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
if (ret)
goto e_free;

- INIT_LIST_HEAD(&sev->regions_list);
-
return 0;

e_free:
@@ -1637,8 +1627,6 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
src->handle = 0;
src->pages_locked = 0;
src->enc_context_owner = NULL;
-
- list_cut_before(&dst->regions_list, &src->regions_list, &src->regions_list);
}

static int sev_es_migrate_from(struct kvm *dst, struct kvm *src)
@@ -1861,115 +1849,13 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
int svm_register_enc_region(struct kvm *kvm,
struct kvm_enc_region *range)
{
- struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
- struct enc_region *region;
- int ret = 0;
-
- if (!sev_guest(kvm))
- return -ENOTTY;
-
- /* If kvm is mirroring encryption context it isn't responsible for it */
- if (is_mirroring_enc_context(kvm))
- return -EINVAL;
-
- if (range->addr > ULONG_MAX || range->size > ULONG_MAX)
- return -EINVAL;
-
- region = kzalloc(sizeof(*region), GFP_KERNEL_ACCOUNT);
- if (!region)
- return -ENOMEM;
-
- mutex_lock(&kvm->lock);
- region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
- if (IS_ERR(region->pages)) {
- ret = PTR_ERR(region->pages);
- mutex_unlock(&kvm->lock);
- goto e_free;
- }
-
- region->uaddr = range->addr;
- region->size = range->size;
-
- list_add_tail(&region->list, &sev->regions_list);
- mutex_unlock(&kvm->lock);
-
- /*
- * The guest may change the memory encryption attribute from C=0 -> C=1
- * or vice versa for this memory range. Lets make sure caches are
- * flushed to ensure that guest data gets written into memory with
- * correct C-bit.
- */
- sev_clflush_pages(region->pages, region->npages);
-
- return ret;
-
-e_free:
- kfree(region);
- return ret;
-}
-
-static struct enc_region *
-find_enc_region(struct kvm *kvm, struct kvm_enc_region *range)
-{
- struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
- struct list_head *head = &sev->regions_list;
- struct enc_region *i;
-
- list_for_each_entry(i, head, list) {
- if (i->uaddr == range->addr &&
- i->size == range->size)
- return i;
- }
-
- return NULL;
-}
-
-static void __unregister_enc_region_locked(struct kvm *kvm,
- struct enc_region *region)
-{
- sev_unpin_memory(kvm, region->pages, region->npages);
- list_del(&region->list);
- kfree(region);
+ return 0;
}

int svm_unregister_enc_region(struct kvm *kvm,
struct kvm_enc_region *range)
{
- struct enc_region *region;
- int ret;
-
- /* If kvm is mirroring encryption context it isn't responsible for it */
- if (is_mirroring_enc_context(kvm))
- return -EINVAL;
-
- mutex_lock(&kvm->lock);
-
- if (!sev_guest(kvm)) {
- ret = -ENOTTY;
- goto failed;
- }
-
- region = find_enc_region(kvm, range);
- if (!region) {
- ret = -EINVAL;
- goto failed;
- }
-
- /*
- * Ensure that all guest tagged cache entries are flushed before
- * releasing the pages back to the system for use. CLFLUSH will
- * not do this, so issue a WBINVD.
- */
- wbinvd_on_all_cpus();
-
- __unregister_enc_region_locked(kvm, region);
-
- mutex_unlock(&kvm->lock);
return 0;
-
-failed:
- mutex_unlock(&kvm->lock);
- return ret;
}

int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
@@ -2018,7 +1904,6 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
mirror_sev->fd = source_sev->fd;
mirror_sev->es_active = source_sev->es_active;
mirror_sev->handle = source_sev->handle;
- INIT_LIST_HEAD(&mirror_sev->regions_list);
ret = 0;

/*
@@ -2038,8 +1923,6 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
void sev_vm_destroy(struct kvm *kvm)
{
struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
- struct list_head *head = &sev->regions_list;
- struct list_head *pos, *q;

WARN_ON(sev->num_mirrored_vms);

@@ -2066,18 +1949,6 @@ void sev_vm_destroy(struct kvm *kvm)
*/
wbinvd_on_all_cpus();

- /*
- * if userspace was terminated before unregistering the memory regions
- * then lets unpin all the registered memory.
- */
- if (!list_empty(head)) {
- list_for_each_safe(pos, q, head) {
- __unregister_enc_region_locked(kvm,
- list_entry(pos, struct enc_region, list));
- cond_resched();
- }
- }
-
sev_unbind_asid(kvm, sev->handle);
sev_asid_free(sev);
}
@@ -2946,13 +2817,90 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 1);
}

+void sev_pin_spte(struct kvm *kvm, gfn_t gfn, enum pg_level level,
+ kvm_pfn_t pfn)
+{
+ struct kvm_arch_memory_slot *aslot;
+ struct kvm_memory_slot *slot;
+ gfn_t rel_gfn, pin_pfn;
+ unsigned long npages;
+ kvm_pfn_t old_pfn;
+ int i;
+
+ if (!sev_guest(kvm))
+ return;
+
+ if (WARN_ON_ONCE(is_error_noslot_pfn(pfn) || kvm_is_reserved_pfn(pfn)))
+ return;
+
+ /* Tested till 1GB pages */
+ if (KVM_BUG_ON(level > PG_LEVEL_1G, kvm))
+ return;
+
+ slot = gfn_to_memslot(kvm, gfn);
+ if (!slot || !slot->arch.pfns)
+ return;
+
+ /*
+ * Use relative gfn index within the memslot for the bitmap as well as
+ * the pfns array
+ */
+ rel_gfn = gfn - slot->base_gfn;
+ aslot = &slot->arch;
+ pin_pfn = pfn;
+ npages = KVM_PAGES_PER_HPAGE(level);
+
+ /* Pin the page, KVM doesn't yet support page migration. */
+ for (i = 0; i < npages; i++, rel_gfn++, pin_pfn++) {
+ if (test_bit(rel_gfn, aslot->pinned_bitmap)) {
+ old_pfn = aslot->pfns[rel_gfn];
+ if (old_pfn == pin_pfn)
+ continue;
+
+ put_page(pfn_to_page(old_pfn));
+ }
+
+ set_bit(rel_gfn, aslot->pinned_bitmap);
+ aslot->pfns[rel_gfn] = pin_pfn;
+ get_page(pfn_to_page(pin_pfn));
+ }
+
+ /*
+ * Flush any cached lines of the page being added since "ownership" of
+ * it will be transferred from the host to an encrypted guest.
+ */
+ clflush_cache_range(__va(pfn << PAGE_SHIFT), page_level_size(level));
+}
+
void sev_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
{
struct kvm_arch_memory_slot *aslot = &slot->arch;
+ kvm_pfn_t *pfns;
+ gfn_t gfn;
+ int i;

if (!sev_guest(kvm))
return;

+ if (!aslot->pinned_bitmap || !slot->arch.pfns)
+ goto out;
+
+ pfns = aslot->pfns;
+
+ /*
+ * Iterate the memslot to find the pinned pfn using the bitmap and drop
+ * the pfn stored.
+ */
+ for (i = 0, gfn = slot->base_gfn; i < slot->npages; i++, gfn++) {
+ if (test_and_clear_bit(i, aslot->pinned_bitmap)) {
+ if (WARN_ON(!pfns[i]))
+ continue;
+
+ put_page(pfn_to_page(pfns[i]));
+ }
+ }
+
+out:
if (aslot->pinned_bitmap) {
kvfree(aslot->pinned_bitmap);
aslot->pinned_bitmap = NULL;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3fb19974f719..22535c680b3f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4743,6 +4743,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {

.alloc_memslot_metadata = sev_alloc_memslot_metadata,
.free_memslot = sev_free_memslot,
+ .pin_spte = sev_pin_spte,
};

static struct kvm_x86_init_ops svm_init_ops __initdata = {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index b2f8b3b52680..c731bc91ea8f 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -77,7 +77,6 @@ struct kvm_sev_info {
unsigned int handle; /* SEV firmware handle */
int fd; /* SEV device fd */
unsigned long pages_locked; /* Number of pages locked */
- struct list_head regions_list; /* List of registered regions */
u64 ap_jump_table; /* SEV-ES AP Jump Table address */
struct kvm *enc_context_owner; /* Owner of copied encryption context */
unsigned long num_mirrored_vms; /* Number of VMs sharing this ASID */
@@ -648,5 +647,7 @@ int sev_alloc_memslot_metadata(struct kvm *kvm,
struct kvm_memory_slot *new);
void sev_free_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot);
+void sev_pin_spte(struct kvm *kvm, gfn_t gfn, enum pg_level level,
+ kvm_pfn_t pfn);

#endif
--
2.32.0