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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> --- 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
