From: Guang Zeng <guang.zeng@xxxxxxxxx> With KVM_CAP_XSAVE, userspace uses a hardcoded 4KB buffer to get/set xstate data from/to KVM. This doesn't work when dynamic xfeatures (e.g. AMX) are exposed to the guest as they require a larger buffer size. Introduce a new capability (KVM_CAP_XSAVE2). Userspace VMM gets the required xstate buffer size via KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2). KVM_SET_XSAVE is extended to work with both legacy and new capabilities by doing properly-sized memdup_user() based on the guest fpu container. KVM_GET_XSAVE is kept for backward-compatible reason. Instead, KVM_GET_XSAVE2 is introduced under KVM_CAP_XSAVE2 as the preferred interface for getting xstate buffer (4KB or larger size) from KVM (Link: https://lkml.org/lkml/2021/12/15/510) Also, update the api doc with the new KVM_GET_XSAVE2 ioctl. Signed-off-by: Guang Zeng <guang.zeng@xxxxxxxxx> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx> Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxx> Signed-off-by: Kevin Tian <kevin.tian@xxxxxxxxx> Signed-off-by: Yang Zhong <yang.zhong@xxxxxxxxx> --- Documentation/virt/kvm/api.rst | 42 ++++++++++++++++++++++++++++-- arch/x86/include/uapi/asm/kvm.h | 16 +++++++++++- arch/x86/kvm/cpuid.c | 2 +- arch/x86/kvm/cpuid.h | 2 ++ arch/x86/kvm/x86.c | 45 ++++++++++++++++++++++++++++++++- include/uapi/linux/kvm.h | 4 +++ 6 files changed, 106 insertions(+), 5 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index f4ea5e41a4d0..d3791a14eb9a 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -1569,6 +1569,7 @@ otherwise it will return EBUSY error. struct kvm_xsave { __u32 region[1024]; + __u32 extra[0]; }; This ioctl would copy current vcpu's xsave struct to the userspace. @@ -1577,7 +1578,7 @@ This ioctl would copy current vcpu's xsave struct to the userspace. 4.43 KVM_SET_XSAVE ------------------ -:Capability: KVM_CAP_XSAVE +:Capability: KVM_CAP_XSAVE and KVM_CAP_XSAVE2 :Architectures: x86 :Type: vcpu ioctl :Parameters: struct kvm_xsave (in) @@ -1588,9 +1589,18 @@ This ioctl would copy current vcpu's xsave struct to the userspace. struct kvm_xsave { __u32 region[1024]; + __u32 extra[0]; }; -This ioctl would copy userspace's xsave struct to the kernel. +This ioctl would copy userspace's xsave struct to the kernel. It copies +as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2), +when invoked on the vm file descriptor. The size value returned by +KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096. +Currently, it is only greater than 4096 if a dynamic feature has been +enabled with ``arch_prctl()``, but this may change in the future. + +The offsets of the state save areas in struct kvm_xsave follow the +contents of CPUID leaf 0xD on the host. 4.44 KVM_GET_XCRS @@ -5535,6 +5545,34 @@ the trailing ``'\0'``, is indicated by ``name_size`` in the header. The Stats Data block contains an array of 64-bit values in the same order as the descriptors in Descriptors block. +4.42 KVM_GET_XSAVE2 +------------------ + +:Capability: KVM_CAP_XSAVE2 +:Architectures: x86 +:Type: vcpu ioctl +:Parameters: struct kvm_xsave (out) +:Returns: 0 on success, -1 on error + + +:: + + struct kvm_xsave { + __u32 region[1024]; + __u32 extra[0]; + }; + +This ioctl would copy current vcpu's xsave struct to the userspace. It +copies as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) +when invoked on the vm file descriptor. The size value returned by +KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096. +Currently, it is only greater than 4096 if a dynamic feature has been +enabled with ``arch_prctl()``, but this may change in the future. + +The offsets of the state save areas in struct kvm_xsave follow the contents +of CPUID leaf 0xD on the host. + + 5. The kvm_run structure ======================== diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 5a776a08f78c..2da3316bb559 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -373,9 +373,23 @@ struct kvm_debugregs { __u64 reserved[9]; }; -/* for KVM_CAP_XSAVE */ +/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */ struct kvm_xsave { + /* + * KVM_GET_XSAVE2 and KVM_SET_XSAVE write and read as many bytes + * as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) + * respectively, when invoked on the vm file descriptor. + * + * The size value returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) + * will always be at least 4096. Currently, it is only greater + * than 4096 if a dynamic feature has been enabled with + * ``arch_prctl()``, but this may change in the future. + * + * The offsets of the state save areas in struct kvm_xsave follow + * the contents of CPUID leaf 0xD on the host. + */ __u32 region[1024]; + __u32 extra[0]; }; #define KVM_MAX_XCRS 16 diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index ba4c3d5d2386..c55e57b30e81 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -32,7 +32,7 @@ u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly; EXPORT_SYMBOL_GPL(kvm_cpu_caps); -static u32 xstate_required_size(u64 xstate_bv, bool compacted) +u32 xstate_required_size(u64 xstate_bv, bool compacted) { int feature_bit = 0; u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET; diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index c99edfff7f82..8a770b481d9d 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -30,6 +30,8 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu, bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, bool exact_only); +u32 xstate_required_size(u64 xstate_bv, bool compacted); + int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu); u64 kvm_vcpu_reserved_gpa_bits_raw(struct kvm_vcpu *vcpu); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 553e4af12edc..92a1ea13ad51 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4314,6 +4314,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) else r = 0; break; + case KVM_CAP_XSAVE2: { + u64 guest_perm = xstate_get_guest_group_perm(); + + r = xstate_required_size(supported_xcr0 & guest_perm, false); + if (r < sizeof(struct kvm_xsave)) + r = sizeof(struct kvm_xsave); + break; + } default: break; } @@ -4917,6 +4925,16 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu, vcpu->arch.pkru); } +static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu, + u8 *state, unsigned int size) +{ + if (fpstate_is_confidential(&vcpu->arch.guest_fpu)) + return; + + fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, + state, size, vcpu->arch.pkru); +} + static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu, struct kvm_xsave *guest_xsave) { @@ -5370,6 +5388,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, break; } case KVM_GET_XSAVE: { + r = -EINVAL; + if (vcpu->arch.guest_fpu.uabi_size > sizeof(struct kvm_xsave)) + break; + u.xsave = kzalloc(sizeof(struct kvm_xsave), GFP_KERNEL_ACCOUNT); r = -ENOMEM; if (!u.xsave) @@ -5384,7 +5406,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, break; } case KVM_SET_XSAVE: { - u.xsave = memdup_user(argp, sizeof(*u.xsave)); + int size = vcpu->arch.guest_fpu.uabi_size; + + u.xsave = memdup_user(argp, size); if (IS_ERR(u.xsave)) { r = PTR_ERR(u.xsave); goto out_nofree; @@ -5393,6 +5417,25 @@ long kvm_arch_vcpu_ioctl(struct file *filp, r = kvm_vcpu_ioctl_x86_set_xsave(vcpu, u.xsave); break; } + + case KVM_GET_XSAVE2: { + int size = vcpu->arch.guest_fpu.uabi_size; + + u.xsave = kzalloc(size, GFP_KERNEL_ACCOUNT); + r = -ENOMEM; + if (!u.xsave) + break; + + kvm_vcpu_ioctl_x86_get_xsave2(vcpu, u.buffer, size); + + r = -EFAULT; + if (copy_to_user(argp, u.xsave, size)) + break; + + r = 0; + break; + } + case KVM_GET_XCRS: { u.xcrs = kzalloc(sizeof(struct kvm_xcrs), GFP_KERNEL_ACCOUNT); r = -ENOMEM; diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 12421e76adcb..6305426f1bc0 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204 #define KVM_CAP_ARM_MTE 205 #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206 +#define KVM_CAP_XSAVE2 207 #ifdef KVM_CAP_IRQ_ROUTING @@ -1621,6 +1622,9 @@ struct kvm_enc_region { #define KVM_S390_NORMAL_RESET _IO(KVMIO, 0xc3) #define KVM_S390_CLEAR_RESET _IO(KVMIO, 0xc4) +/* Available with KVM_CAP_XSAVE2 */ +#define KVM_GET_XSAVE2 _IOR(KVMIO, 0xcf, struct kvm_xsave) + struct kvm_s390_pv_sec_parm { __u64 origin; __u64 length;
