Re: [PATCH 21/34] KVM: x86: Add support for "protected VMs" that can utilize private memory

From: Fuad Tabba
Date: Mon Nov 06 2023 - 06:02:41 EST

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Hi,

On Sun, Nov 5, 2023 at 4:33 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> 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

(replied to v13 earlier, sorry)

nit: "that isn't"

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

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>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Message-Id: <20231027182217.3615211-24-seanjc@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@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 4a9a291380ad..38882263278d 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
> @@ -8766,6 +8785,19 @@ 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 75ab0da06e64..a565a2e70f30 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -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
> 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 e61383674c75..c1716e83d176 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 f521c97f5c64..6d0772b47041 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -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;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 8eb10f560c69..e9cb2df67a1d 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -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
>
> 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
> --
> 2.39.1
>
>

Next message: Fuad Tabba: "Re: [PATCH 22/34] KVM: selftests: Drop unused kvm_userspace_memory_region_find() helper"
Previous message: David Laight: "RE: mach-socfpga: PCIe Root IO TLP support for Cyclone V"
In reply to: Paolo Bonzini: "[PATCH 21/34] KVM: x86: Add support for "protected VMs" that can utilize private memory"
Next in thread: Paolo Bonzini: "[PATCH 22/34] KVM: selftests: Drop unused kvm_userspace_memory_region_find() helper"
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