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kvm: x86: Add support for getting/setting expanded xstate buffer

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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@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-19-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Guang Zeng 2022-01-05 04:35:29 -08:00 committed by Paolo Bonzini
parent c60427dd50
commit be50b2065d
6 changed files with 106 additions and 5 deletions
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42
Documentation/virt/kvm/api.rst
View File

@ -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
========================

16
arch/x86/include/uapi/asm/kvm.h
View File

@ -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

2
arch/x86/kvm/cpuid.c
View File

@ -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;

2
arch/x86/kvm/cpuid.h
View File

@ -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);

45
arch/x86/kvm/x86.c
View File

@ -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;

4
include/uapi/linux/kvm.h
View File

@ -1132,6 +1132,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_ARM_MTE 205
#define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
#define KVM_CAP_VM_GPA_BITS 207
#define KVM_CAP_XSAVE2 208
#ifdef KVM_CAP_IRQ_ROUTING
@ -1622,6 +1623,9 @@ 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;