Re: [PATCH v13 23/35] KVM: x86: Add support for "protected VMs" that can utilize private memory

From: Paolo Bonzini
Date: Mon Nov 06 2023 - 06:04:03 EST

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On 11/6/23 12:00, Fuad Tabba wrote:

Hi,

On Fri, Oct 27, 2023 at 7:23 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:

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

nit: "that isn't"

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
Tested-by: Fuad Tabba <tabba@xxxxxxxxxx>

Hi Fuad,

thanks for your reviews and tests of the gmem patches! Can you please continue replying to v14?

Thanks,

Paolo

Cheers,
/fuad

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@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 32 ++++++++++++++++++++++++++++++++
arch/x86/include/asm/kvm_host.h | 15 +++++++++------
arch/x86/include/uapi/asm/kvm.h | 3 +++
arch/x86/kvm/Kconfig | 12 ++++++++++++
arch/x86/kvm/mmu/mmu_internal.h | 1 +
arch/x86/kvm/x86.c | 16 +++++++++++++++-
include/uapi/linux/kvm.h | 1 +
virt/kvm/Kconfig | 5 +++++
8 files changed, 78 insertions(+), 7 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 38dc1fda4f45..00029436ac5b 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -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
@@ -8650,6 +8669,19 @@ 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
=========================

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f9e8d5642069..dff10051e9b6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1244,6 +1244,7 @@ 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;
@@ -2077,6 +2078,12 @@ 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;
@@ -2125,14 +2132,10 @@ 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
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 1a6a1f987949..a448d0964fc0 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -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 */
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 091b74599c22..8452ed0228cb 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -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
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 86c7cb692786..b66a7d47e0e4 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -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;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c4d17727b199..e3eb608b6692 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4441,6 +4441,13 @@ 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;
@@ -4632,6 +4639,11 @@ 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;
}
@@ -12314,9 +12326,11 @@ 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;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 29e9eb51dec9..5b5820d19e71 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1218,6 +1218,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_MEMORY_FAULT_INFO 231
#define KVM_CAP_MEMORY_ATTRIBUTES 232
#define KVM_CAP_GUEST_MEMFD 233
+#define KVM_CAP_VM_TYPES 234

#ifdef KVM_CAP_IRQ_ROUTING

diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 08afef022db9..2c964586aa14 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -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
--
2.42.0.820.g83a721a137-goog

Next message: syzbot: "Re: [syzbot] [PATCH] Test for 2030579113a1"
Previous message: Fuad Tabba: "Re: [PATCH 23/34] KVM: selftests: Convert lib's mem regions to KVM_SET_USER_MEMORY_REGION2"
In reply to: Fuad Tabba: "Re: [PATCH v13 23/35] KVM: x86: Add support for "protected VMs" that can utilize private memory"
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