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

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.

Guang Zeng committed 4 years ago

Commit be50b201 parent c60427d6 files · +106 −5Browse files

Unified · Split

6 files

Documentation/virt/kvm/api.rst +40 −2
arch/x86/include/uapi/asm/kvm.h +15 −1
arch/x86/kvm/cpuid.c +1 −1
arch/x86/kvm/cpuid.h +2 −0
arch/x86/kvm/x86.c +44 −1
include/uapi/linux/kvm.h +4 −0

Documentation/virt/kvm/api.rst+40−2

@@ -1569,6 +1569,7 @@ otherwise it will return EBUSY error. · 1568 unmodified lines
1569	1569
1570	1570	struct kvm_xsave {
1571	1571	__u32 region[1024];
	1572	+ __u32 extra[0];
1572	1573	};
1573	1574
1574	1575	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. · 2 unmodified lines
1577	1578	4.43 KVM_SET_XSAVE
1578	1579	------------------
1579	1580
1580		−:Capability: KVM_CAP_XSAVE
	1581	+:Capability: KVM_CAP_XSAVE and KVM_CAP_XSAVE2
1581	1582	:Architectures: x86
1582	1583	:Type: vcpu ioctl
1583	1584	:Parameters: struct kvm_xsave (in)
@@ -1588,9 +1589,18 @@ This ioctl would copy current vcpu's xsave struct to the userspace. · 4 unmodified lines
1588	1589
1589	1590	struct kvm_xsave {
1590	1591	__u32 region[1024];
	1592	+ __u32 extra[0];
1591	1593	};
1592	1594
1593		−This ioctl would copy userspace's xsave struct to the kernel.
	1595	+This ioctl would copy userspace's xsave struct to the kernel. It copies
	1596	+as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2),
	1597	+when invoked on the vm file descriptor. The size value returned by
	1598	+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
	1599	+Currently, it is only greater than 4096 if a dynamic feature has been
	1600	+enabled with ``arch_prctl()``, but this may change in the future.
	1601	+
	1602	+The offsets of the state save areas in struct kvm_xsave follow the
	1603	+contents of CPUID leaf 0xD on the host.
1594	1604
1595	1605
1596	1606	4.44 KVM_GET_XCRS
@@ -5535,6 +5545,34 @@ the trailing ``'\0'``, is indicated by ``name_size`` in the header. · 3938 unmodified lines
5535	5545	The Stats Data block contains an array of 64-bit values in the same order
5536	5546	as the descriptors in Descriptors block.
5537	5547
	5548	+4.42 KVM_GET_XSAVE2
	5549	+------------------
	5550	+
	5551	+:Capability: KVM_CAP_XSAVE2
	5552	+:Architectures: x86
	5553	+:Type: vcpu ioctl
	5554	+:Parameters: struct kvm_xsave (out)
	5555	+:Returns: 0 on success, -1 on error
	5556	+
	5557	+
	5558	+::
	5559	+
	5560	+ struct kvm_xsave {
	5561	+ __u32 region[1024];
	5562	+ __u32 extra[0];
	5563	+ };
	5564	+
	5565	+This ioctl would copy current vcpu's xsave struct to the userspace. It
	5566	+copies as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
	5567	+when invoked on the vm file descriptor. The size value returned by
	5568	+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
	5569	+Currently, it is only greater than 4096 if a dynamic feature has been
	5570	+enabled with ``arch_prctl()``, but this may change in the future.
	5571	+
	5572	+The offsets of the state save areas in struct kvm_xsave follow the contents
	5573	+of CPUID leaf 0xD on the host.
	5574	+
	5575	+
5538	5576	5. The kvm_run structure
5539	5577	========================
5540	5578

arch/x86/include/uapi/asm/kvm.h+15−1

@@ -373,9 +373,23 @@ struct kvm_debugregs { · 372 unmodified lines
373	373	__u64 reserved[9];
374	374	};
375	375
376		−/* for KVM_CAP_XSAVE */
	376	+/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */
377	377	struct kvm_xsave {
	378	+ /*
	379	+ * KVM_GET_XSAVE2 and KVM_SET_XSAVE write and read as many bytes
	380	+ * as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
	381	+ * respectively, when invoked on the vm file descriptor.
	382	+ *
	383	+ * The size value returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
	384	+ * will always be at least 4096. Currently, it is only greater
	385	+ * than 4096 if a dynamic feature has been enabled with
	386	+ * ``arch_prctl()``, but this may change in the future.
	387	+ *
	388	+ * The offsets of the state save areas in struct kvm_xsave follow
	389	+ * the contents of CPUID leaf 0xD on the host.
	390	+ */
378	391	__u32 region[1024];
	392	+ __u32 extra[0];
379	393	};
380	394
381	395	#define KVM_MAX_XCRS 16

arch/x86/kvm/cpuid.c+1−1

@@ -32,7 +32,7 @@ · 31 unmodified lines
32	32	u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
33	33	EXPORT_SYMBOL_GPL(kvm_cpu_caps);
34	34
35		−static u32 xstate_required_size(u64 xstate_bv, bool compacted)
	35	+u32 xstate_required_size(u64 xstate_bv, bool compacted)
36	36	{
37	37	int feature_bit = 0;
38	38	u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;

arch/x86/kvm/cpuid.h+2−0

@@ -30,6 +30,8 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu, · 29 unmodified lines
30	30	bool kvm_cpuid(struct kvm_vcpu vcpu, u32 eax, u32 *ebx,
31	31	u32 ecx, u32 edx, bool exact_only);
32	32
	33	+u32 xstate_required_size(u64 xstate_bv, bool compacted);
	34	+
33	35	int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu);
34	36	u64 kvm_vcpu_reserved_gpa_bits_raw(struct kvm_vcpu *vcpu);
35	37

arch/x86/kvm/x86.c+44−1

@@ -4314,6 +4314,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) · 4313 unmodified lines
4314	4314	else
4315	4315	r = 0;
4316	4316	break;
	4317	+ case KVM_CAP_XSAVE2: {
	4318	+ u64 guest_perm = xstate_get_guest_group_perm();
	4319	+
	4320	+ r = xstate_required_size(supported_xcr0 & guest_perm, false);
	4321	+ if (r < sizeof(struct kvm_xsave))
	4322	+ r = sizeof(struct kvm_xsave);
	4323	+ break;
	4324	+ }
4317	4325	default:
4318	4326	break;
4319	4327	}
@@ -4917,6 +4925,16 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu, · 597 unmodified lines
4917	4925	vcpu->arch.pkru);
4918	4926	}
4919	4927
	4928	+static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
	4929	+ u8 *state, unsigned int size)
	4930	+{
	4931	+ if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
	4932	+ return;
	4933	+
	4934	+ fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
	4935	+ state, size, vcpu->arch.pkru);
	4936	+}
	4937	+
4920	4938	static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
4921	4939	struct kvm_xsave *guest_xsave)
4922	4940	{
@@ -5370,6 +5388,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp, · 447 unmodified lines
5370	5388	break;
5371	5389	}
5372	5390	case KVM_GET_XSAVE: {
	5391	+ r = -EINVAL;
	5392	+ if (vcpu->arch.guest_fpu.uabi_size > sizeof(struct kvm_xsave))
	5393	+ break;
	5394	+
5373	5395	u.xsave = kzalloc(sizeof(struct kvm_xsave), GFP_KERNEL_ACCOUNT);
5374	5396	r = -ENOMEM;
5375	5397	if (!u.xsave)
@@ -5384,7 +5406,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, · 8 unmodified lines
5384	5406	break;
5385	5407	}
5386	5408	case KVM_SET_XSAVE: {
5387		− u.xsave = memdup_user(argp, sizeof(*u.xsave));
	5409	+ int size = vcpu->arch.guest_fpu.uabi_size;
	5410	+
	5411	+ u.xsave = memdup_user(argp, size);
5388	5412	if (IS_ERR(u.xsave)) {
5389	5413	r = PTR_ERR(u.xsave);
5390	5414	goto out_nofree;
@@ -5393,6 +5417,25 @@ long kvm_arch_vcpu_ioctl(struct file *filp, · 2 unmodified lines
5393	5417	r = kvm_vcpu_ioctl_x86_set_xsave(vcpu, u.xsave);
5394	5418	break;
5395	5419	}
	5420	+
	5421	+ case KVM_GET_XSAVE2: {
	5422	+ int size = vcpu->arch.guest_fpu.uabi_size;
	5423	+
	5424	+ u.xsave = kzalloc(size, GFP_KERNEL_ACCOUNT);
	5425	+ r = -ENOMEM;
	5426	+ if (!u.xsave)
	5427	+ break;
	5428	+
	5429	+ kvm_vcpu_ioctl_x86_get_xsave2(vcpu, u.buffer, size);
	5430	+
	5431	+ r = -EFAULT;
	5432	+ if (copy_to_user(argp, u.xsave, size))
	5433	+ break;
	5434	+
	5435	+ r = 0;
	5436	+ break;
	5437	+ }
	5438	+
5396	5439	case KVM_GET_XCRS: {
5397	5440	u.xcrs = kzalloc(sizeof(struct kvm_xcrs), GFP_KERNEL_ACCOUNT);
5398	5441	r = -ENOMEM;

include/uapi/linux/kvm.h+4−0

@@ -1132,6 +1132,7 @@ struct kvm_ppc_resize_hpt { · 1131 unmodified lines
1132	1132	#define KVM_CAP_ARM_MTE 205
1133	1133	#define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
1134	1134	#define KVM_CAP_VM_GPA_BITS 207
	1135	+#define KVM_CAP_XSAVE2 208
1135	1136
1136	1137	#ifdef KVM_CAP_IRQ_ROUTING
1137	1138
@@ -1622,6 +1623,9 @@ struct kvm_enc_region { · 484 unmodified lines
1622	1623	#define KVM_S390_NORMAL_RESET _IO(KVMIO, 0xc3)
1623	1624	#define KVM_S390_CLEAR_RESET _IO(KVMIO, 0xc4)
1624	1625
	1626	+/* Available with KVM_CAP_XSAVE2 */
	1627	+#define KVM_GET_XSAVE2 _IOR(KVMIO, 0xcf, struct kvm_xsave)
	1628	+
1625	1629	struct kvm_s390_pv_sec_parm {
1626	1630	__u64 origin;
1627	1631	__u64 length;

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

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