[PATCH 18/34] KVM: x86/mmu: Handle page fault for private memory
From: Paolo Bonzini
Date: Sun Nov 05 2023 - 11:34:36 EST
From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
Add support for resolving page faults on guest private memory for VMs
that differentiate between "shared" and "private" memory. For such VMs,
KVM_MEM_PRIVATE memslots can include both fd-based private memory and
hva-based shared memory, and KVM needs to map in the "correct" variant,
i.e. KVM needs to map the gfn shared/private as appropriate based on the
current state of the gfn's KVM_MEMORY_ATTRIBUTE_PRIVATE flag.
For AMD's SEV-SNP and Intel's TDX, the guest effectively gets to request
shared vs. private via a bit in the guest page tables, i.e. what the guest
wants may conflict with the current memory attributes. To support such
"implicit" conversion requests, exit to user with KVM_EXIT_MEMORY_FAULT
to forward the request to userspace. Add a new flag for memory faults,
KVM_MEMORY_EXIT_FLAG_PRIVATE, to communicate whether the guest wants to
map memory as shared vs. private.
Like KVM_MEMORY_ATTRIBUTE_PRIVATE, use bit 3 for flagging private memory
so that KVM can use bits 0-2 for capturing RWX behavior if/when userspace
needs such information, e.g. a likely user of KVM_EXIT_MEMORY_FAULT is to
exit on missing mappings when handling guest page fault VM-Exits. In
that case, userspace will want to know RWX information in order to
correctly/precisely resolve the fault.
Note, private memory *must* be backed by guest_memfd, i.e. shared mappings
always come from the host userspace page tables, and private mappings
always come from a guest_memfd instance.
Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
Tested-by: Fuad Tabba <tabba@xxxxxxxxxx>
Message-Id: <20231027182217.3615211-21-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 8 ++-
arch/x86/kvm/mmu/mmu.c | 101 ++++++++++++++++++++++++++++++--
arch/x86/kvm/mmu/mmu_internal.h | 1 +
include/linux/kvm_host.h | 8 ++-
include/uapi/linux/kvm.h | 1 +
5 files changed, 110 insertions(+), 9 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 6d681f45969e..4a9a291380ad 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6953,6 +6953,7 @@ spec refer, https://github.com/riscv/riscv-sbi-doc.
/* KVM_EXIT_MEMORY_FAULT */
struct {
+ #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 3)
__u64 flags;
__u64 gpa;
__u64 size;
@@ -6961,8 +6962,11 @@ spec refer, https://github.com/riscv/riscv-sbi-doc.
KVM_EXIT_MEMORY_FAULT indicates the vCPU has encountered a memory fault that
could not be resolved by KVM. The 'gpa' and 'size' (in bytes) describe the
guest physical address range [gpa, gpa + size) of the fault. The 'flags' field
-describes properties of the faulting access that are likely pertinent.
-Currently, no flags are defined.
+describes properties of the faulting access that are likely pertinent:
+
+ - KVM_MEMORY_EXIT_FLAG_PRIVATE - When set, indicates the memory fault occurred
+ on a private memory access. When clear, indicates the fault occurred on a
+ shared access.
Note! KVM_EXIT_MEMORY_FAULT is unique among all KVM exit reasons in that it
accompanies a return code of '-1', not '0'! errno will always be set to EFAULT
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f5c6b0643645..754a5aaebee5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3147,9 +3147,9 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
return level;
}
-int kvm_mmu_max_mapping_level(struct kvm *kvm,
- const struct kvm_memory_slot *slot, gfn_t gfn,
- int max_level)
+static int __kvm_mmu_max_mapping_level(struct kvm *kvm,
+ const struct kvm_memory_slot *slot,
+ gfn_t gfn, int max_level, bool is_private)
{
struct kvm_lpage_info *linfo;
int host_level;
@@ -3161,6 +3161,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
break;
}
+ if (is_private)
+ return max_level;
+
if (max_level == PG_LEVEL_4K)
return PG_LEVEL_4K;
@@ -3168,6 +3171,16 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
return min(host_level, max_level);
}
+int kvm_mmu_max_mapping_level(struct kvm *kvm,
+ const struct kvm_memory_slot *slot, gfn_t gfn,
+ int max_level)
+{
+ bool is_private = kvm_slot_can_be_private(slot) &&
+ kvm_mem_is_private(kvm, gfn);
+
+ return __kvm_mmu_max_mapping_level(kvm, slot, gfn, max_level, is_private);
+}
+
void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
struct kvm_memory_slot *slot = fault->slot;
@@ -3188,8 +3201,9 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
* Enforce the iTLB multihit workaround after capturing the requested
* level, which will be used to do precise, accurate accounting.
*/
- fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
- fault->gfn, fault->max_level);
+ fault->req_level = __kvm_mmu_max_mapping_level(vcpu->kvm, slot,
+ fault->gfn, fault->max_level,
+ fault->is_private);
if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
return;
@@ -4269,6 +4283,55 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL);
}
+static inline u8 kvm_max_level_for_order(int order)
+{
+ BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
+
+ KVM_MMU_WARN_ON(order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G) &&
+ order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M) &&
+ order != KVM_HPAGE_GFN_SHIFT(PG_LEVEL_4K));
+
+ if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
+ return PG_LEVEL_1G;
+
+ if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
+ return PG_LEVEL_2M;
+
+ return PG_LEVEL_4K;
+}
+
+static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
+ struct kvm_page_fault *fault)
+{
+ kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT,
+ PAGE_SIZE, fault->write, fault->exec,
+ fault->is_private);
+}
+
+static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
+ struct kvm_page_fault *fault)
+{
+ int max_order, r;
+
+ if (!kvm_slot_can_be_private(fault->slot)) {
+ kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+ return -EFAULT;
+ }
+
+ r = kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault->pfn,
+ &max_order);
+ if (r) {
+ kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+ return r;
+ }
+
+ fault->max_level = min(kvm_max_level_for_order(max_order),
+ fault->max_level);
+ fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
+
+ return RET_PF_CONTINUE;
+}
+
static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
struct kvm_memory_slot *slot = fault->slot;
@@ -4301,6 +4364,14 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
return RET_PF_EMULATE;
}
+ if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
+ kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+ return -EFAULT;
+ }
+
+ if (fault->is_private)
+ return kvm_faultin_pfn_private(vcpu, fault);
+
async = false;
fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
fault->write, &fault->map_writable,
@@ -7188,6 +7259,26 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
}
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
+ struct kvm_gfn_range *range)
+{
+ /*
+ * Zap SPTEs even if the slot can't be mapped PRIVATE. KVM x86 only
+ * supports KVM_MEMORY_ATTRIBUTE_PRIVATE, and so it *seems* like KVM
+ * can simply ignore such slots. But if userspace is making memory
+ * PRIVATE, then KVM must prevent the guest from accessing the memory
+ * as shared. And if userspace is making memory SHARED and this point
+ * is reached, then at least one page within the range was previously
+ * PRIVATE, i.e. the slot's possible hugepage ranges are changing.
+ * Zapping SPTEs in this case ensures KVM will reassess whether or not
+ * a hugepage can be used for affected ranges.
+ */
+ if (WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm)))
+ return false;
+
+ return kvm_unmap_gfn_range(kvm, range);
+}
+
static bool hugepage_test_mixed(struct kvm_memory_slot *slot, gfn_t gfn,
int level)
{
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index decc1f153669..86c7cb692786 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -201,6 +201,7 @@ struct kvm_page_fault {
/* Derived from mmu and global state. */
const bool is_tdp;
+ const bool is_private;
const bool nx_huge_page_workaround_enabled;
/*
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a6de526c0426..67dfd4d79529 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2357,14 +2357,18 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
#define KVM_DIRTY_RING_MAX_ENTRIES 65536
static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
- gpa_t gpa, gpa_t size)
+ gpa_t gpa, gpa_t size,
+ bool is_write, bool is_exec,
+ bool is_private)
{
vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
vcpu->run->memory_fault.gpa = gpa;
vcpu->run->memory_fault.size = size;
- /* Flags are not (yet) defined or communicated to userspace. */
+ /* RWX flags are not (yet) defined or communicated to userspace. */
vcpu->run->memory_fault.flags = 0;
+ if (is_private)
+ vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_PRIVATE;
}
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2802d10aa88c..8eb10f560c69 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -535,6 +535,7 @@ struct kvm_run {
} notify;
/* KVM_EXIT_MEMORY_FAULT */
struct {
+#define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 3)
__u64 flags;
__u64 gpa;
__u64 size;
--
2.39.1