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KVM: x86: Add support for "protected VMs" that can utilize private memory

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Add a new x86 VM type, KVM_X86_SW_PROTECTED_VM, to serve as a development
and testing vehicle for Confidential (CoCo) VMs, and potentially to even
become a "real" product in the distant future, e.g. a la pKVM.

The private memory support in KVM x86 is aimed at AMD's SEV-SNP and
Intel's TDX, but those technologies are extremely complex (understatement),
difficult to debug, don't support running as nested guests, and require
hardware that's isn't universally accessible.  I.e. relying SEV-SNP or TDX
for maintaining guest private memory isn't a realistic option.

At the very least, KVM_X86_SW_PROTECTED_VM will enable a variety of
selftests for guest_memfd and private memory support without requiring
unique hardware.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20231027182217.3615211-24-seanjc@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-10-27 11:22:05 -07:00 committed by Paolo Bonzini
parent eed52e434b
commit 89ea60c2c7
8 changed files with 78 additions and 7 deletions
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32
Documentation/virt/kvm/api.rst
View File

@ -147,10 +147,29 @@ described as 'basic' will be available.
The new VM has no virtual cpus and no memory.
You probably want to use 0 as machine type.
X86:
^^^^
Supported X86 VM types can be queried via KVM_CAP_VM_TYPES.
S390:
^^^^^
In order to create user controlled virtual machines on S390, check
KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL as
privileged user (CAP_SYS_ADMIN).
MIPS:
^^^^^
To use hardware assisted virtualization on MIPS (VZ ASE) rather than
the default trap & emulate implementation (which changes the virtual
memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
flag KVM_VM_MIPS_VZ.
ARM64:
^^^^^^
On arm64, the physical address size for a VM (IPA Size limit) is limited
to 40bits by default. The limit can be configured if the host supports the
extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use
@ -8765,6 +8784,19 @@ block sizes is exposed in KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES as a
64-bit bitmap (each bit describing a block size). The default value is
0, to disable the eager page splitting.
8.41 KVM_CAP_VM_TYPES
---------------------
:Capability: KVM_CAP_MEMORY_ATTRIBUTES
:Architectures: x86
:Type: system ioctl
This capability returns a bitmap of support VM types. The 1-setting of bit @n
means the VM type with value @n is supported. Possible values of @n are::
#define KVM_X86_DEFAULT_VM 0
#define KVM_X86_SW_PROTECTED_VM 1
9. Known KVM API problems
=========================

15
arch/x86/include/asm/kvm_host.h
View File

@ -1255,6 +1255,7 @@ enum kvm_apicv_inhibit {
};
struct kvm_arch {
unsigned long vm_type;
unsigned long n_used_mmu_pages;
unsigned long n_requested_mmu_pages;
unsigned long n_max_mmu_pages;
@ -2089,6 +2090,12 @@ void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd);
void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
int tdp_max_root_level, int tdp_huge_page_level);
#ifdef CONFIG_KVM_PRIVATE_MEM
#define kvm_arch_has_private_mem(kvm) ((kvm)->arch.vm_type != KVM_X86_DEFAULT_VM)
#else
#define kvm_arch_has_private_mem(kvm) false
#endif
static inline u16 kvm_read_ldt(void)
{
u16 ldt;
@ -2137,14 +2144,10 @@ enum {
#define HF_SMM_INSIDE_NMI_MASK (1 << 2)
# define KVM_MAX_NR_ADDRESS_SPACES 2
/* SMM is currently unsupported for guests with private memory. */
# define kvm_arch_nr_memslot_as_ids(kvm) (kvm_arch_has_private_mem(kvm) ? 1 : 2)
# define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? 1 : 0)
# define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm)
static inline int kvm_arch_nr_memslot_as_ids(struct kvm *kvm)
{
return KVM_MAX_NR_ADDRESS_SPACES;
}
#else
# define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, 0)
#endif

3
arch/x86/include/uapi/asm/kvm.h
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@ -562,4 +562,7 @@ struct kvm_pmu_event_filter {
/* x86-specific KVM_EXIT_HYPERCALL flags. */
#define KVM_EXIT_HYPERCALL_LONG_MODE BIT(0)
#define KVM_X86_DEFAULT_VM 0
#define KVM_X86_SW_PROTECTED_VM 1
#endif /* _ASM_X86_KVM_H */

12
arch/x86/kvm/Kconfig
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@ -77,6 +77,18 @@ config KVM_WERROR
If in doubt, say "N".
config KVM_SW_PROTECTED_VM
bool "Enable support for KVM software-protected VMs"
depends on EXPERT
depends on X86_64
select KVM_GENERIC_PRIVATE_MEM
help
Enable support for KVM software-protected VMs. Currently "protected"
means the VM can be backed with memory provided by
KVM_CREATE_GUEST_MEMFD.
If unsure, say "N".
config KVM_INTEL
tristate "KVM for Intel (and compatible) processors support"
depends on KVM && IA32_FEAT_CTL

1
arch/x86/kvm/mmu/mmu_internal.h
View File

@ -297,6 +297,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
.max_level = KVM_MAX_HUGEPAGE_LEVEL,
.req_level = PG_LEVEL_4K,
.goal_level = PG_LEVEL_4K,
.is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
};
int r;

16
arch/x86/kvm/x86.c
View File

@ -4548,6 +4548,13 @@ static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
return 0;
}
static bool kvm_is_vm_type_supported(unsigned long type)
{
return type == KVM_X86_DEFAULT_VM ||
(type == KVM_X86_SW_PROTECTED_VM &&
IS_ENABLED(CONFIG_KVM_SW_PROTECTED_VM) && tdp_enabled);
}
int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
{
int r = 0;
@ -4739,6 +4746,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_X86_NOTIFY_VMEXIT:
r = kvm_caps.has_notify_vmexit;
break;
case KVM_CAP_VM_TYPES:
r = BIT(KVM_X86_DEFAULT_VM);
if (kvm_is_vm_type_supported(KVM_X86_SW_PROTECTED_VM))
r |= BIT(KVM_X86_SW_PROTECTED_VM);
break;
default:
break;
}
@ -12436,9 +12448,11 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
int ret;
unsigned long flags;
if (type)
if (!kvm_is_vm_type_supported(type))
return -EINVAL;
kvm->arch.vm_type = type;
ret = kvm_page_track_init(kvm);
if (ret)
goto out;

1
include/uapi/linux/kvm.h
View File

@ -1227,6 +1227,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_MEMORY_FAULT_INFO 232
#define KVM_CAP_MEMORY_ATTRIBUTES 233
#define KVM_CAP_GUEST_MEMFD 234
#define KVM_CAP_VM_TYPES 235
#ifdef KVM_CAP_IRQ_ROUTING

5
virt/kvm/Kconfig
View File

@ -104,3 +104,8 @@ config KVM_GENERIC_MEMORY_ATTRIBUTES
config KVM_PRIVATE_MEM
select XARRAY_MULTI
bool
config KVM_GENERIC_PRIVATE_MEM
select KVM_GENERIC_MEMORY_ATTRIBUTES
select KVM_PRIVATE_MEM
bool